t-w..
V . • • ' ;i
B&g!
PI
IkIIS
■
... ' . • > if- , 70 / , , | . > r .y
. v - . ‘J'/'-y-
' ■/-// #707y=y
/ , , ; , •■ . ■ , 3 * ;•. * > ■ / >.
0 . * / =/- / / / V' ' / . , ' / /’//■'
\ * / - .-•
f',.7
' '
01 hjr-J
■
( , ", . . t
. . v ■ '//./■/, //,
. ■ ///>* / '
< ■ ■ :
'
■ ' /> // V -
' ' ' ' / ' ' - / *
■ , '/ '/// / .’/////;.
','///// > / // / .
"
/ , ,
■' ' / / / ' * * t ■
' •* '• / / / / / / / ,
• f ///•/,/..
■ ■ ' ^ / / / / / / / / ■
• * / ■- / / / / / ,• / ... .. '
: •' f S / / / / z ' / ' •
• ; ’■ / / f / f. / t
- ' ■'•//////.<.,
' ■ '• ' ' 7 f f t / , -
•• t ? f / ' * / / .• ,
' ' / / '' ^ • * f !
’ ' ( * f * ///////,, ,
f / / / // j ■ * f f '/ y / / / *
' / " / / t / ////t /
'///// f * ' f * * f * * /■'/.- . / /' -■
' / / t ‘ f f / / / / / * ■ - , if
• f ;
■' f
'// ' ' ' " ^ ' •' / -• / ; , ' ; '//
/ r ' / *
‘ / < ‘Iff/!/: - . - •
f * * f f ./•
f > f f >'
. ra^P^««Bi^es^# >C_ - ,^Hr , . , 4
7;J^J
I
.V
I
Digitized by the Internet Archive
in 2017 with funding from
Wellcome Library
https://archive.org/details/b29329875_0001
\
THE
ELEMENTS
OF
EXPERIMENTAL CHEMISTRY,
BY
WILLIAM HENRY, M.D. F.R.S.
Vice-Pres. of the Lit. and Phil. Soc. at Manchester; Member of the Roy.
Med. and Wernerian Societies at Edinburgh; the Medico-Chirurgical
and Geological Societies of London ; the Physical Soc. of
Jena ; the Nat. Hist. Soc. of Moscow, &c.
THE EIGHTH EDITION,
COMPREHENDING ALL THE RECENT DISCOVERIES ; AND ILLUSTRATED
WITH NINE PLATES BY LOWRY.
VOL. I.
LONDON:
PRINTED FOR BALDWIN, CRADOCK, AND JOY,
47, PATERNOSTER-ROW?
AND R. HUNTER, SUCCESSOR TO JOHNSON,
st. Paul’s church yard.
1818
historical j
\ MEDICAL /
L. Baldwin, Printer,
Kevv Bridge-street, London
TO
MR. JOHN DALTON,
President of the Lit. and Phil. Soc. of Manchester; Member of tiie Academy
of Sciences of the Royal Institute of France ; &c.
AS A
TESTIMONY OF RESPECT
FOR TUB
ZEAL, DISINTERESTEDNESS, AND SUCCESS,
WITH WHICH
HE HAS DEVOTED HIMSELF TO THE ADVANCEMENT OF
CHEMICAL PHILOSOPHY,
THIS WORK IS INSCRIBED,
BY HIS FRIEND
THE AUTHOR.
Manchester ,
Oct. 1318.
ADVERTISEMENT
TO THE
EIGHTH EDITION,
DURING the interval which has elapsed since the pub¬
lication of the last edition of this work, the progress of
Chemistry, though not distinguished by essential changes in
the general principles of the science, has nevertheless been
marked, not only by beneficial applications of those principles
to the useful arts, but by the discovery of a great number of
important facts, and of some new and interesting bodies.
Among practical inventions, the Safety Lamp of Sir Hum¬
phry Davy stands pre-eminent, as a contribution from science
to the interests of humanity, not resulting from accident, but
suggested by general reasoning, and perfected by an admirable
train of philosophical induction. — To our knowledge of indi¬
vidual bodies has been added that of a new alkali, a new
earth, and two new metals; of a gas which, like chlorine,
becomes acidified by union with hydrogen ; of new acids,
composed of oxygen in combination with chlorine, with ni¬
trogen, and with phosphorus ; and of compounds, before un¬
discovered, derived from the vegetable and animal kingdoms.
In a variety of instances, the properties of bodies, that had
been long known, have been better ascertained, and more
extensively investigated. Such additional evidence, too, of
the nature of chlorine has arisen out of the further contro¬
versy respecting it, as to have satisfied me of the propriety of
a change in its classification. It has been necessary, there¬
fore, again to revise the whole work with the greatest care ; to
VI
ADVERTISEMENT.
make considerable additions to many of the sections ; and to
introduce a few entirely new ones. In a chapter of addenda,
also, at the close of the second volume, the history of disco¬
veries will be found continued to the latest period which the
publication would admit. To gain room for these improve¬
ments, without much enlarging the bulk of the volumes, I have
rejected every thing which recent experience has corrected or
rendered doubtful.
Though no pains have been spared to render the work a
faithful abstract of the present state of Chemistry, yet it is
not improbable that errors and omissions may still be disco¬
vered in it. In rectifying these, I hope to be assisted by a
continuance of those candid criticisms, both through public
and private channels of communication, to which I have al¬
ready been greatly indebted.
Manchester ,
Oct . 1818.
CONTENTS OF VOL. I.
/
Page
Introduction . . v
PART I.
An arranged Series oe Experiments and Processes
TO BE PERFORMED BY THE STUDENT OF CHEMISTRY.
CHAP. I. Of a Chemical Laboratory and Appa¬
ratus. . . 1
CHAP. II. Of Chemical Affinity . 14
Sect. I. Of Cohesion , Solution , and Crystalli¬
zation. . . . . . 15
II. Of Chemical Affinity , and the general
Phenomena of Chemical Action. ... 24?
III. Of the Proportions in which Bodies
combine ; and of the Atomic Theory 28
IV. Of Elective Affinity . . . . . 38
V. Of the Causes , which modify the Action
of Chemical Affinity . 40
VI. Of the Estimation of the Forces of
Affinity . . . 50
VII. Of Complex Affinity . . 53
VIII. Experimental Illustrations of Chemical
Affinity , Solution , fyc . 58
CHAP. III. Of Heat or Caloric . 64
Sect. I. General Observations on Heat . . ibid.
II. Illustrations of the Effects of Free
Caloric . . 72
III. Caloric the Cause of Fluidity . . . 91
IV . — — — Vapour ........ 96
CONTENTS.
vm
Page
CHAP. III. Sect. V. Specific Caloric . . . . 109
CHAP. IV. Of Light . . . . . . . . . . 112
CHAP. V9 Of Gases. . . . . 119
Sect. I. Of the Apparatus for Gases . ibid.
Classification of' Gases . 130
II. Oxygen Gas. . . . . . . 135
III. Chlorine Gas . . 142
IV. Niti 'ogen or Azotic Gas . 144
V. Atmospheric Air . 148
VI. Hydrogen Gas . . 154
CHAP. VI. Of the Composition, Decomposition, and
Properties of Water . 166
Sect. I. Synthesis, or Composition of Water. . ibid,
II. Analysis, or Decomposition of Water . 171
III. Properties and Effects of Water .... 174
CHAP. VII. On the Chemical Agencies of Common
and Galvanic Electricity . 183
Sect. I. Of the Construction of Galvanic Ar¬
rangements . 184
II. On the mutual Relation of Electricity
and Galvanism . 191
III. On the Chemical Agencies of Electri¬
city and Galvanism . 193
IV. Theory of the Changes produced by
Galvanic Electricity . 202
V. Theory of the Action of the Galvanic
v Pile . 205
CHAP. VIII, Alkalies. Their General Qualities. . 212
Sect. I. Pure Potash and PureSoda . ibid.
Art. 1. Their preparation and gene¬
ral Qualities . 212
Hydrated Alkalies ........ 213
2. Analysis of the two fixed Al¬
kalies. . . 216
3. Potassium.. . 212
Potassureted Hydrogen Gas . 229
4. Sodium . . 230
II. Lithia, or Lithina . . 233
III. Pure Ammonia . . 236
CHAP. VIII, Sect. III. Art. 1. Preparation and Qualities
of Ammonia ........ 236
2. Electrical Analysis of
Ammonia . . 240
3. On the Presence of Oxy¬
gen in Ammonia ; and
on the Amalgam of
Mercury and Ammonia 243
4. Action of Potassium on
Ammonia . . 246
CHAP. IX. Earths . . . . . . 249
Sect. I. Barytes . 252
II. Strontites „ . 255
HI. Lime . 257
IV. Magnesia . 260
V. Silex . 261
VI. Alumine . 265
VII. Zircon . . . 268
*VI II. Glucine . . 269
IX. Yttria, or Ittria . 270
X. Tkorina . 272
CHAP. X. Of Acids in general . 275
CHAP. XI. Carbonic Acid and its Base.- — Car¬
bonates. — Binary Compounds of
Carbon . 283
Sect. I. Carbon and Charcoal . ibid.
II. Combustion of Carbon . 287
III. Carbonic Acid . 290
IV. Carbonates ..................... 299
Art . 1. Sub-carbonate and Carbon¬
ate of potash . ibid.
2. Carbonate of Soda . . 304
3. Sub-carbonate and Bi-carbo¬
nate of Ammonia ...... 305
4. Carbonate of Barytes ..... 309
5. . — . Strontites.... 311
6. * - — - — — Lime. ....... 312
7. — - Magnesia .... 315
8. — - -* - Glucine . 316
V. Gaseous Oxide of Carbon , or Car¬
bon oris Oxide. ................. ibid.
X
CONTENTS.
Page
CHAP. XI, Sect. VI. Combination of Carbon with Hydro¬
gen , forming Carbureted. Hydro¬
gen Gas , or Hydro- Carburet .... SI 9
On the Fire-Damp of Coal Mines ,
and the Construction and Principle
of the Safety Lamp , of Sir H. Davy 324
VII. Carburet of Hydrogen , or Cyanogen 327
CHAP. XII. Sulphur, —Sulphuric Acid,— Sulphates,
— Binary Compounds oe Sulphur . . . 323
Sect. I. Sulphur . . . . „ . . „ ibidm
II. Sulphuric Acid . . 333
III. Sulphurous Acid Gas . . . 341
IV. Combination of Sulphuric Acid with
Alkalies . . 344
Art. 1. SVphate of Potash . ibid .
2. - - — Seda ........ 346
3. — - — Ammonia .... 347
4. - — - Barytes . . 348
5. - - — . — — Strontites .... 351
«■
6. - - — — - — Lime. ....... 352
7. - — - Magnesia .... 353
8. - — — — - - Alumina .... 355
9. . — _ — _____ Glucine . 358
10. Sulphate of Zircon . ibid.
11. — - — - Yttria . ibid.
V. Sulphites . 359
VI. Binary Compounds of Sulphur. — ■
1 sty with Alkalies 2t/, with Hy¬
drogen . . 362
Art. 1. Sulphurets . . . . . ibid.
2. Sulphureted Hydrogen Gas 365
3. Hydro-Sulphurets . 369
4. Super-Sulphureted Hydro¬
gen, and Hydroguretted
Sulphurets . 371
Sulphuret of Carbon, or Al¬
cohol of Sulphur . 37 5
CHAPo XIII. Combination of Nitrogen with Oxygen,
constituting Nitric Acid, — Nitrous
Gas, — Nitrous Oxide,— and Compounds
of Nitric Acid with Alkalies . 379
Page
CHAP, XIIL Sect, I. Nitric Acid . . . , . 383
II. Nitrous Gas, or Nitric Oxide . 390
III. Gaseous Oxide of Nitrogen— -Nitrous
Oxide of Davy . . . s 398
IV, Nitrous Acid . . . 403
V. Per-nitrous Acid . ...» 405
VI. Nitrates . . 406
Art, 1. Nitrate of Potash. ......... ibid.
2. , , - Soda . . 413
3. . — ... — — — Ammonia . ibid.
4. - Barytes ......... 414
5„ — - Strontites ....... 415
5. . . . Lime ........... ibid.
7. „ — — _ Magnesia . . . 416
8. — Alumine ........ 417
9. Glucine. . . ibid.
10. — — — — Zircon .......... ibid.
11. . . . — - Yttria .......... 417
VII. Nitrites . . 418
CHAP, XIV. Muriatic Acid,— Oxymuriatic Acid, or
*
Chlorine,— and their Compounds .... 419
Muriatic Acid. . . . „. . . ibid.
Sect. I. Compound of Chlorine with Hydrogen 42 i
II. Compound of Chlorine with Oxygen ,
— Oxides of Chlorine , — Chloric
Acid, — Per-ch loric Acid ......... 431
Chlorine with Oxygen, Euchlorine ibid.
Per-oxide of Chlorine ........ 4S2
Chloric Acid . . 433
III. Chlorine with Nitrogen. ........... 537
IV . Chlorine with the Metals of the Alka¬
lies and Earths, and with the Oxides
of these Metals . . 438
V . Chlorine with Charcoal, Carbonic Ox¬
ide, and Carbureted Hydrogen . . . 439
VI. Chlorine with Sulphur and its Com¬
pounds . . . . 441
VII. Chlorine with the Metals . . ibid.
Nomenclature of the Compounds
of Muriatic and Oxymuriatic
Acids . . . . . 442
CONTENTS.
xh
Page
CHAP. XIV. Sect. VIII. Muriates {Hydro-Chlorates) . 444
Art 1. Muriate of Potash . . ibid.
2. - — - Soda . 445
3. Ammonia .... 447
4. - - — Barytes . 449
5. — - Strontites .... 450
6. - • Lime . 451
7. - — - Magnesia . 453
8. — — — — — Alumine ..... ibid.
9. _ — — — Glucine . ibid.
10. ■■■ , ' i Zircon . . ibid.
11. Muriate of Yttria . 454
IX. Chlorates or Hyper -oxy -Muriates . . ibid.
Art. 1. Chlorate or Hyper-oxy-
Muriate of Potash. ..... ibid •
2. Chlorate of Soda . 459
3. — ■■ Ammonia. . . . ibid.
4. Chlorates with earthy Bases. 460
(1.) Chlorate of Barytes . . ibid.
{2.) — — - Strontites. 461
(3.) - ■ Lime. . . . ibid.
X. Nitro-Muriatic Acid . 462
XI. Murio- Sulphuric Acid, . . 463
APPENDIX.
Description of the Plates . . . 465
INTRODUCTION *.
It has so long been a custom to preface a course of lectures
with the history of the science which is their subject, that it
may be necessary to state, briefly, the reasons that have in¬
duced me to depart from this established usage.
The history of chemistry may either be merely a history of
the science, that is, a view of the progressive development of
the facts and doctrines of which the science is composed ; or
it may comprehend, also, the biography of chemists. The
detail of the progress of discovery,' however, concerning par¬
ticular objects of chemical research, would certainly be pre¬
mature, at a period, when the student may be supposed to
be ignorant of the external forms, and even of the existence,
of no inconsiderable part of them. Respecting chemists them¬
selves, little can be said that can contribute to information or
amusement ; for their lives, devoted to the abstract pursuits
of science, have seldom been productive of events, that are
suited to awaken or gratify general curiosity. Our interest,
indeed, respecting philosophers, is seldom excited, unless by
a knowledge of the additions which they have made to the
* The following discourse formed, originally, the introduction to a series
of lectures delivered in Manchester, and was afterwards published under
the title of “ A General View of the Nature and Objects of Chemistry, and
of its Application to Arts and Manufactures As the readers of an
elementary book may be presumed to require a similar plan of instruction,
with the hearers of a popular course of lectures, I have thought it unneces¬
sary to alter the form under which the essay first appeared, though a few
passages are applicable chiefly to the persons to whom it was originally ad¬
dressed.
XIV
INTRODUCTION.
facts or theories of a science ; and with these a lecturer rnav
fairly presume, however the fact may really be, that his
hearers, at the commencement of a course, are wholly un¬
acquainted. On these grounds, therefore, I hope to be ex¬
cused for devoting to other purposes the time, that would
have been allotted to the history of the science. For this,
will be substituted a brief view of the nature and objects of
chemistry ; of its connexion with the arts and with other
(
sciences ; and an outline of the plan on which the following
lectures will be conducted.
Natural philosophy, in its most extensive sense, is a term
comprehending every science, that has for its objects the pro¬
perties and affections of matter. But it has attained, by the
sanction of common language, a more limited signification ;
and chemistry, though strictly a branch of natural philo¬
sophy, is generally regarded as a distinct science. Between
the two it may, perhaps, be difficult to mark out precisely the
line of separation : but, an obvious character of the facts of
natural philosophy is, that they are always attended with
sensible motion ; and the determination of the laws of motion
is peculiarly the office of its cultivators. Chemical changes,
on the other hand, of the most important kind, often take
place without any apparent motion, either of the mass, or of
it's minute parts ; and where the eye is unable to perceive that
any change has occurred. The laws of gravitation, of cen¬
tral forces, and all the other powers that fall under the cogni¬
zance of the natural philosopher, produce, at most, only a
change of place in the bodies that obey their influence. Biit,
in chemical changes, we may always observe an important
difference in the properties of things : their appearances and
qualities are completely altered, and their individuality de¬
stroyed. Thus, two highly corrosive substances, by uniting
chemically together, may become mild and harmless ; the
combination of two colourless substances may present us with
a compound of brilliant complexion ; and the union of two
fluids, with a compact and solid mass.
INTRODUCTION.
XV
Chemistry, therefore, may be defined, that science, the ob¬
ject of which is to discover and explain the changes of com¬
position that occur among* the integrant and constituent parts
of different bodies *.
From this definition, it may readily be conceived, how
wide is the range of chemical inquiry ; and, by applying it to
the various events that daily occur in the order of nature, we
shall be enabled to separate them with accuracy, and to allot,
to the sciences of natural philosophy and chemistry, the proper
objects of the cultivation of each. Whenever a change of
place is a necessary part of any event, we shall call in the aid
of the former. When this condition may be dispensed with,
we shall resort to chemistry for the light of its principles.
But it will be often found, that the concurrence of the two
sciences is essential to the full explanation ol phenomena.
The water of the ocean, for example, is raised into the atmo¬
sphere by its chemical combination with the matter of heat ;
but the clouds, that are thus formed, maintain their elevated
situation by virtue of a specific gravity inferior to that of the
lower regions of the air, — a law, the discovery and application
of which are due to the natural philosopher, strictly so called.
It has not been unusual to consider chemistry, under the
twofold view of a science and of an art. This arrangement,
O 7
however, appears to have had its origin in an imperfect dis¬
crimination between two objects, that are essentially distinct.
Science consists of assemblages of facts, associated together in
classes, according to circumstances of resemblance or analogy.
The business of its cultivators is, first, to investigate and
establish individual truths, either by the careful observation
of natural appearances, or of new and artificial combinations
of phenomena produced by the instruments of experiment.
The next step is the induction, from well ascertained facts,
* The reader, who wishes to examine other definitions of chemistry, will
find a variety of them, collected by Dr. Black, in the first volume of his
a Lectures/7 published, since his death, by Professor Robison.
5
XVI
INTRODUCTION.
of general principles or laws, more or less comprehensive in-
their extent, and serving, like the classes and orders of
natural history, the purposes of an artifical arrangement. Of
such a body of facts and doctrines, the science of chemistry is
composed. But the employment of the artist consists merely
in producing a given effect, for the most part by the sole
guidance of practice or experience. In the repetition of pro¬
cesses, he has only to follow an established rule ; and, in the
improvement of his art, he is benefited generally by fortuitous
combinations, to which he has not been directed by any
general axiom. An artist, indeed, of enlarged and en¬
lightened mind, may avail himself of general principles, and
may employ them as an useful instrument in perfecting esta¬
blished operations : but the art and the science are still marked
by a distinct boundary. In such hands, they are auxiliaries
to eacli other; the one contributing a valuable accession of
facts ; and the other, in return, imparting fixed and compre¬
hensive principles, which simplify the processes of art, and
direct to new and important practices.
The possession of the general principles of chemistry en¬
ables us to comprehend the mutual relation of a great variety
of events, that form a part of the established course of nature.
It unfolds the most sublime views of the beauty and harmony
of the universe ; and developes a plan of vast extent, and of
uninterrupted order, which could have been conceived only
by perfect wisdom, and executed by unbounded power. By
withdrawing the mind, also, from pursuits and amusements
that excite the imagination, its investigations may tend, in
common with the rest of the physical sciences, to the improve¬
ment of our intellectual and moral habits ; to strengthen the
faculty of patient and accurate thinking ; and to substitute
placid trains of feeling, for those which are too apt to be
awakened by the contending interests of men in society, or
the imperfect government of our own passions.
The class of natural events that call for the explana¬
tion of chemical science, is of very considerable extent ; and
6
INTRODUCTION.
XVII
the natural philosopher (using this term in its common ac¬
ceptation) is wholly incompetent to unfold their connexion.
He may explain, for example, on the principles of his own
science, the annual and diurnal revolutions of the Earth, and
part of the train of consequences depending on these rotations.
But here he must stop ; and the chemist must trace the effects,
on the Earth’s surface, of the caloric and light derived from
the sun ; the absorption of caloric by the various bodies on
which it falls ; the consequent fluidity of some, and volatiliza¬
tion of others ; the production of clouds, and their condensa¬
tion in the form of rain ; and the effects of this rain, as well as
of the sun’s heat, on the animal, vegetable, and mineral king¬
doms. In these minuter changes, we shall find, there is not
less excellence of contrivance, than in the stupendous move¬
ments of the planetary system. And they interest us even
more nearly ; because, though not more connected with our
existence or comfort, yet they are more within our sphere of
observation ; and an acquaintance with their laws admits of
a more direct application to human affairs.
There is another branch of knowledge (that of natural
history), which is materially advanced by the application of
chemical science. The classifications of the naturalist are
derived from an examination and comparison of the external
forms, both of animate and inanimate bodies. He distributes
the whole range of nature into three great and comprehensive
kingdoms, —the animal, the vegetable, and the mineral. Each
of these, again, is subdivded into several less extensive classes ;
and individual objects are referred to their place in the system,
by the agreement of their characters, with those assigned to
the class, order, and genus. In the different departments of
natural history, these resemblances vary in distinctness, in
facility of observation, and in certainty of description. Thus,
the number and disposition of the parts of fructification in
vegetables afford marks of discrimination, which are well
defined, and easily ascertained. But minerals, that are not
voh L b
XV11I
INTRODUCTION.
possessed of a regularly crystallized form, are distinguished
by outward qualities that scarcely admit of being accurately
conveyed by language ; such as minute shades of colour ; or
trifling differences of hardness, transparency, See. To the
evidence of these loose and varying characters, that of the
chemical composition of minerals has within the few past years
been added ; and mineralogy has been advanced, from a con¬
fused assemblage of its objects, to -the dignity of a well me¬
thodized and scientific system. In the example of crystal¬
lized bodies, the correspondence between external form and
chemical composition, has been most successfully traced by
the genius of Haiiy ; whose method of investigation has
enabled him, in numerous instances, to anticipate, from phy¬
sical characters, the results of the most skilful and laborious
analysis.
It is unnecessary to pursue this part of the subject to a
greater extent ; because, to all who have been in the habit of
philosophical investigation, the connexion between the sci¬
ences must be sufficiently apparent ; and because there is
another ground, on which chemistry is more likely to claim,
with success, the respect and attention of the great mass of
mankind. This is, its capacity of ministering to our wants
and our luxuries, and of instructing us to convert to the or¬
dinary purposes of life, many substances which nature pre¬
sents in a rude and useless form. The extraction of metals
from their ores ; the conversion of the rudest materials into
the beautiful fabrics of glass and porcelain ; the production of
wine, ardent spirits, and vinegar; and the dyeing of linen,
cotton, and woollen manufactures,— -are only a few of the arts
that are dependent on chemistry for their improvement, and
even for their successful practice.
It cannot, however, be denied, that all the arts which have
been mentioned were practised in times when the rank of che¬
mistry, as a science, was extremely degraded ; and that they
are the daily employment of unlettered and ignorant men.
INTRODUCTION.
NIX
But to what does this confession amount ? and how far does
it prove the independence of the above arts on the science of
chemistry ?
The skill of an artist is compounded of knowledge and of
manual dexterity. The latter, it is obvious, no science can
teach. But the acquirement of experience, in other words,
a talent for the accurate observation of facts, and the habit of
arranging facts in the best manner, may be greatly facilitated
by the possession of scientific principles. Indeed, it is hardly
possible for any one to frame rules for the practice of a che¬
mical art, or to profit by the rules of others, wrho is unac¬
quainted with the general doctrines of the science. For, in,
all rules, it is implied, that the promised effect will only take
place, when circumstances are precisely the same as in the
case under which the rule was formed. To ensure an un¬
erring uniformity of result, the substances, employed in che¬
mical processes, must be of uniform composition and excel¬
lence ; or, when it is not possible to obtain them thus un¬
varied, the artist should be able to judge precisely of the
defect, that he may proportion his agents according to their
qualities. Were chemical knowledge more generally pos¬
sessed, we should hear less of failures and disappointments in
chemical operations ; and the artist would commence his pro¬
ceedings, not, as at present, with distrust and uncertainty,
but with a confident and well grounded expectation of
success.
It will scarcely be contended, that any one of the arts has
hitherto attained the extent of its possible perfection. In all,
there is yet a wide scope for improvement, and an extensive
range for ingenuity and invention. But from what class of
men are we to expect useful discoveries ? Are we to trust, as
hitherto, to the favour of chance and accident ; to the for¬
tuitous success of those who are not guided in their experi¬
ments by any general principles ? Or shall we not rather
endeavour to inform the artist, and induce him to substitute,
for vague and random conjecture, the torch of induction and
b 2
XX
INTRODUCTION.
of rational analogy? In the present imperfect state of his
knowledge, the artist is even unable fully to avail himself of
those fortunate accidents, by which improvements sometimes
occur in his processes ; because, to the eye of common ob¬
servation, he may have acted agreeably to established rules,
and have varied in circumstances which he can neither per¬
ceive nor appreciate. The man of science, in these instances,
sees more deeply, and, by availing himself of a minute and
accidental difference, contributes at once to the promotion of
his own interest, and to the advancement of his art.
But it is the union of theory with practice that is now re¬
commended. And “ when theoretical knowledge and prac¬
tical skill are happily combined in the same person, the in¬
tellectual power of man appears in its full perfection, and
equally fits him to conduct, with a masterly hand, the details
of ordinary business, and to contend successfully with the un¬
tried difficulties of new and perplexing situations. In con¬
ducting the former, mere experience may frequently be a
sufficient guide ; but experience and speculation must be com¬
bined to prepare us for the latter*.” “ Expert men,” says
Lord Bacon, “ can execute and judge of particulars one by
one ; but the general counsels, and the plots, and the mar¬
shalling of affairs, come best from those that are learned.”
This recommendation to artists, of the acquirement of sci¬
entific knowledge, is happily sanctioned by the illustrious
success, in our own days, of the application of theory to the
practice of certain arts. Few persons are ignorant of the
benefits, that have resulted to the manufactures of this country,
from the inventions of Mr. Watt and Mr. Wedgwood ; both
of whom have been not less benefactors of philosophy than
eminent for practical skill. The former, by a clear insight
into the doctrine of latent heat, resulting, in a great measure,
from his own acuteness and patience of investigation, and
* Stewart’s Elements of the Philosophy of the Human Mind, chap. ir.
sect. 7.
INTRODUCTION,
XXI
seconded by an unusual share of mechanical skill, has per¬
haps brought the steam-engine to its acme of perfection,
Mr. Wedgwood, aided by the possession of extensive chemical
knowledge, made rapid advances in the improvement of the
art of manufacturing porcelain ; and, besides raising himself
to great opulence and distinction, has created for his country
a source of most profitable and extensive industry. In an
art, also, which is nearly connected with the manufactures of
our own town, and the improvement of which must, there¬
fore, ce come home to our business and bosoms,” we owe un¬
speakable obligations to two speculative chemists, — to Scheele,
who first discovered the oxygenized muriatic acid ; and to
Berthollet, who first instructed us in its application to the art
of bleaching.
Examples, however, may be urged against indulgence in
theory ; and instances are not wanting, in which the love of
speculative refinement has withdrawn men entirely from the
straight path of useful industry, and led them on gradually
to the ruin of their fortunes. But from such instances, it
would be unfair to deduce a general condemnation of theo-
retical knowledge. It would be the common error of arguing
against things that are useful, from their occasional abuse.—
In truth, projects which have, for their foundation, a depend¬
ence on chemical principles, may be undertaken with a more
rational confidence, than such as have in view the accomplish¬
ment of mechanical purposes ; because, in chemistry, we are
better able, than in mechanics, to predict, from an experi¬
ment on a small scale, the probable issue of more extensive
attempts. No one, from the successful trial of a small ma¬
chine, can affirm, with unerring certainty, that the same suc¬
cess will attend one on a greatly enlarged plan ; because the
amount of the resistances, that are opposed to motion, in¬
creases often in a ratio greater than, from theory, could ever
have been foreseen : but the same law, by which the mineral
alkali is extracted from a pound of common salt, must equally
operate on a thousand times the quantity ; and, even when we
XXII
INTRODUCTION.
augment our quantities in this immense degree, the chemical
affinities, by which so large a mass is decomposed, are exerted
only between very small particles. The failures of the me-
chanic, therefore, arise from the nature of things ; they occur,
because he has not in his power the means of foreseeing and
calculating the causes that produce them. But, if the chemist
fail in perfecting an economical scheme on a large scale, it is
either because he has not sufficiently ascertained his facts on
a small one, or has rashly embarked in extensive speculations,
without having previously ensured the accuracy of his esti¬
mates.
The benefits which we are entitled to expect from the efforts
of the artist and the man of science, united in one person,
and at the same time tempered and directed by prudential
wisdom, affect not only individual but national prosperity. To
the support of its distinction, as a commercial nation, this
country is to look for the permanency of its riches, its power,
and, perhaps, even of its liberties ; and this pre-eminence is
to be maintained, not only by local advantages, but on the
more certain ground of superiority in the productions of its
arts. Impressed with a full conviction of this influence of
the sciences, a neighbouring and rival people offer the most
public and respectful incitements to the application of theory
in the improvement of the chemical arts ; and, with the view
of promoting this object, national institutions have been
formed among them, which have been already, in several in¬
stances, attended with the most encouraging success. It may
be sufficient, at present, to mention, as an example, that
France, during a long war, supplied, from her own native
resources, her enormous, and, perhaps, unequalled consump¬
tion of nitre.
The general uses of chemistry have been thus fully en¬
larged upon, because it is a conviction of the utility of the
science, that can alone recommend it to attentive and per¬
severing study. It may now be proper to point out, in detail,
a few of its more striking applications.
INTRODUCTION.
XX1U
I. The art which is, of all others, the most interesting, from
its subserviency to wants that are interwoven with our nature,
is agriculture, or the art of obtaining, from the earth, the
largest crops of useful vegetables at the smallest expense.
The vegetable kingdom agrees with the animal one, in the
possession of a living principle. Every individual of this
kingdom is regularly organized, and requires for its support an
unceasing supply of food, which is converted, as in the animal
body, into substances of various forms and qualities. Each
plant has its periods of growth, health, disease, decay, and
death ; and is affected, in most of these particulars, by the
varying condition of external circumstances. A perfect state
of agricultural knowledge would require, therefore, not only
a minute acquaintance with the structure and economy of
vegetables, but with the nature and effects of the great variety
of external agents, that contribute to their nutriment, or in¬
fluence their state of health and vigour. It can hardly be
expected, that the former attainment will ever be generally
made by practical farmers ; and it is in bringing the agricul¬
turist acquainted with the precise composition of soils and
manures, that chemistry promises the most solid advantages.
Indeed, any knowledge that can be acquired on this subject,
without the aid of chemistry, must be vague and indistinct*
and can neither enable its possessor to produce an intended
effect with certainty, nor be communicated to others in lan»
guage sufficiently intelligible. Thus wre are told, by Mr.
Arthur Young, that, in some parts of England, any loose
clay is called marl, in others marl is called chalk, and in
others clay is called loam. From so confused an application
of terms, all general benefits of experience in agriculture must
be greatly limited.
Chemistry may, to agriculturists, become a universal lan¬
guage, in which the facts, that are observed in this art, may
be so clothed, as to be intelligible to all ages and nations. It
would be desirable, for example, when a writer speaks of clay,
loam, or marl, that he should explain his conception of these
terms, by stating the chemical composition of each substance
XXIV
INTRODUCTION.
expressed by them. For, all the variety of soils and manures,
and all the diversified productions of the vegetable kingdom,
are capable of being resolved, by chemical analysis, into a
small number of elementary ingredients. The formation of a
well defined language, expressing the proportion of these
elements in the various soils and manures, now so vaguely
characterized, would give an accuracy and precision, hitherto
unknown, to the experience of the tillers of the earth.
It has been said, by those who contend for pure empiricism
in the art of agriculture, that it has remained stationary,
notwithstanding all improvements in the sciences, for more
than two thousand years. (6 To refute this assertion,” says
Mr. Kirwan, 66 we need only compare the writings of Cato,
Columella, or Pliny, with many modern tracts, or still better,
with the modern practice of our best farmers.” — “ If the
exact connection of effects with their causes,” he adds, “ has
not been so fully and extensively traced in this as in other
subjects, we must attribute it to the peculiar difficulty of the
investigation. In other subjects, exposed to the joint oper¬
ation of many causes, the effect of each, singly and exclusively
taken, may be particularly examined, and the experimenter
may work in his laboratory, with the object always in his
view*. But the secret processes of vegetation take place in the
dark, exposed to the various and indeterminable influences of
the atmosphere, and require, at least, half a year for their
completion. Hence the difficulty of determining on what
peculiar circumstance success or failure depends ; for, the
diversified experience of many years can alone afford a ra¬
tional foundation for solid, specific conclusions*.”
II. To those who study medicine as a branch of general
science, or with the more important view of practical utility,
chemistry may be recommended with peculiar force and pro¬
priety. — The animal body may be regarded as a living ma¬
chine, obeying the same laws of motion as are daily exempli-
* See Kirwan on Manures.
INTRODUCTION.
XXV
fled in the productions of human art. The arteries are long,
flexible, and elastic canals, admitting, in some measure, the
application of the doctrine of hydraulics ; and the muscles are
so many levers, of precisely the same effect with those which
are employed to gain power in mechanical contrivances.
But there is another view, in which, with equal justice, the
living body may be contemplated. It is a laboratory, in
which are constantly going forward processes of various kinds,
dependent on the operation of chemical affinities. The con¬
version of the various kinds of food into blood, a fluid of com¬
paratively uniform composition and qualities ; the production
of animal heat by the action of the air on that fluid, as it
passes through the lungs ; and the changes, which the blood
afterwards undergoes in its course through the body, — are all,
exclusively, subjects of chemical inquiry. To these, and
many other questions of physiology, chemistry has of late
years been applied with the most encouraging success ; and
it is to a long continued prosecution of the same plan, that
we are to look for a system of physiological science, which
shall derive new vigour and lustre from the passing series of
years.
It must be acknowledged, however, as has been observed
by Sir H. Davy*, that “ the connexion of chemistry with
physiology has given rise to some visionary and seductive
theories; yet even this circumstance has been useful to the
public mind, in exciting it by doubt, and in leading it to
new investigations. A reproach, to a certain degree just, has
been thrown upon those doctrines known by the name of the
chemical physiology; for, in the applications of them, spe¬
culative philosophers have been guided rather by the ana¬
logies of words than of facts. Instead of endeavouring slowly
to lift up the veil, which conceals the wonderful phenomena of
living nature; full of ardent imaginations, they have vainly
and presumptuously attempted to tear it asunder.”
* In his excellent u Discourse, Introductory to a Course of Lectures/’
&c. London. Johnson. 1802.
XXVI
INTRODUCTION®
III. There is an extensive class of arts, forming, when
viewed collectively, a great part of the objects of human
industry, which do not, on a loose and hasty observation,
present any general principle of dependency or connexion.
But they appear thus disunited, because we have been accus¬
tomed to attend only to the productions of these arts, which
are, in truth, subservient to widely different purposes. Who
would conceive, for instance, that iron and common salt ; the
one a metal, the use of which results from its hardness, duc¬
tility, and malleability ; the other a substance, chiefly valuable
from its acting as a preservative and seasoner of food, — are
furnished by arts alike dependent on the general principles of
chemistry? The application of science, in discovering the
principles of these arts, constitutes what has been termed
economical chemistry ; amongst the numerous objects of
which, the following stand most distinguished :
1st. Metallurgy , or the art of extracting metals from their
ores, comprehending that of Assayings by which we are
enabled to judge, from the composition of a small portion, of
the propriety of working large and extensive strata. To the
metallurgist, also, belong the various modifications of the
metals when obtained, and the union of them together, in
different proportions, so as to afford compounds adapted to
particular uses. — Throughout the whole of this art, much
practical knowledge may be suggested by attention to the
general doctrines of chemistry. The artist may receive use¬
ful hints respecting the construction of furnaces for the fusion
of ores and metals; the employment of the proper fluxes: the
utility of the admission or exclusion of air; and the con-
*
version of the refuse of his several operations to useful pur¬
poses. When the metals have been separated from their
ores, they are to be again subjected to various chemical pro¬
cesses. Cast or pig iron is to be changed into the forms of
wrought or malleable iron and of steel. Copper, by com¬
bination with zinc or tin, affords the various compounds of
brass, pinchbeck, bell-metal, gun-metal, &c. Even the art of
printing owes something of its present unexampled perfection
to the improvement of the metal of types.
INTRODUCTION. XXvii
2d. Chemistry is the foundation of those arts that furnish
us with saline substances , an order of bodies highly useful in
the business of common life. Among these, the most con¬
spicuous are, sugar in all its various forms; the vegetable
and mineral alkalies, known in commerce by the names of
potash, pearlasli, and barilla; common salt; green and blue
vitriol, and alum ; nitre or saltpetre ; sugar of lead 5 borax ;
and a long catalogue, which it is needless to extend farther.
3d. The manufacturer of glass, and of various kinds of
pottery and porcelain , should be thoroughly acquainted with
the nature of the substances he employs : with their fusibility,
as affected by difference of proportion, or by the admixture of
foreign ingredients ; with the means of regulating and mea¬
suring high degrees of heat; with the principles on which
depend the hardness of his products, and their fitness for
bearing the vicissitudes of heat and cold ; and with the che¬
mical properties of the best adapted colours and glazings.—
Even the humble art of making bricks and tiles has received,
from the chemical knowledge of Bergman, the addition of se¬
veral interesting facts.
4th. The preparation of various kinds of fermented liquors ,
of wine, and ardent spirits, is intimately connected with che¬
mical principles. Malting, the first step in the production of
some of these liquors, consists in the conversion of part of the
grain into saccharine matter, essential in most instances to the
success of the fermentative change. To acquire a precise ac¬
quaintance with the circumstances, that favour or retard the
process of fermentation, no small share of chemical know¬
ledge is required. The brewer should be able to ascertain,
and to regulate exactly, the strength of his infusions, which
will vary greatly when he has seemingly followed the same
routine. He should be aware of the influence of minute
changes of temperature in retarding or advancing ferment¬
ation ; of the means of promoting it by proper ferments ; and
of the influence of the presence or exclusion of atmospherical
air. A complete acquaintance with the chemical principles
XXV111
INTRODUCTION,
of his art, can hardly fail to afford him essential aid in its
practice.
The production of ardent spirits is only a sequel of the
vinous fermentation, and is, therefore, alike dependent on the
doctrines of chemistry.
5th. The arts of bleaching , dyeing , and printing , are,
throughout, a tissue of chemical operations. It is not unusual
to hear the new mode of bleaching distinguished by the ap¬
pellation of the chemical method ; but it is, in truth, not more
dependent on the principles of this science, than the one which
it has superseded, nor than the kindred arts of dyeing and
printing. In the instance of bleaching, the obligation due to
the speculative chemist is universally felt and acknowledged.
But the dyer and the printer have yet to receive from the phi¬
losopher some splendid invention, which shall command their
respect, and excite their attention to chemical science. From
purely speculative men, however, much less is to be expected,
than from men of enlightened experience, who endeavour to
discover the design and reason of each step in the processes of
their arts, and fit themselves for more effectual observation of
particular facts, by diligently possessing themselves of general
truths.
The objects of inquiry that present themselves to the dyer
and printer, are of considerable number and importance.
The preparation of goods for the reception of colouring
matter ; the application of the best bases, or means of fixing
fugitive colours ; the improvement of colouring ingredients
themselves ; and the means of rendering them permanent, so
that they shall not be affected by soap, or by the accidental
contact of acids or other corrosive bodies: are among: the
subjects of chemical investigation. It is the business of the
dyer, therefore, to become a chemist ; and he may be assured
that, even if no brilliant discovery should be the reward of the
acquisition, he will yet be better fitted by it for conducting
common operations, with certain and unvaried success.
6 th. The tanning and preparation of leather are processes
INTRODUCTION.
xxix
strictly chemical, which were involved in mystery till they
were reduced to well established principles by the researches
of Sequin, and by the subsequent experiments of Davy. In
this, as in most other examples, the application of science to
the practical improvement of an art, has to encounter the b-
stacles of ignorance and prejudice. But the interests of nmn.
are sure finally to prevail ; and the most bigotted attachment
established forms must give place to the clearly demonstrated
utility of new practices. Such d ration is generally
furnished by some artist r‘r -.tore eoh iteiied views than his
neighbours, who has the pirit to deviate from ordinary rules ;
and thus becomes (not unfrequently with some personal sacri¬
fice) a model for the imitation of others, and an important
benefactor of mankind.
Many other chemical arts might be enumerated ; but
enough, I trust, has been said, to evince the connexion between
practical skill and the possession of scientific knowledge. I
shall now proceed to develope the plan, on which the fol¬
lowing course of instruction will be conducted.
There are two methods of delivering the general doctrines
of chemistry, and the facts connected with them. The one
consists in a historical detail of the gradual progress of the
science; and, in pursuing this plan, we follow the natural
progress of the human mind, ascending from particular facts
to the establishment of general truths. But a strong objection
to its adoption is, that we are thus led into a minuteness of
detail, which is ill suited to the plan of elementary instruction.
In the other mode of arrangement, we neglect wholly the
order of time in which facts were discovered, and class them
under general divisions so framed as to assist the mind in ap¬
prehending and retaining the almost infinite variety of parti¬
cular truths.
In a classification of the objects of chemistry, we may
either begin writh those substances, which are deemed to be
simple, and proceed gradually to the more complicated : — or
we may take bodies, as they are usually presented to us, and
arrange them according to the resemblances of their external
XXX
INTRODUCTION.
characters; making the development of their composition a
subordinate part of the plan. To the former, or synthetic
method, ther e is this strong objection, — that as we are proba¬
bly still very remote from a knowledge of the true elements
of i fitter, it mst be liable, in the progress of science, to fre¬
quent and fundamental changes. It has been found necessary,
for example, in* consequence of Sir H. Davy’s discoveries, to
remove the fixed alkalies and the earths from the class of simple
to that of comneund bodies. Besides, it may be urged, where
are we to place uurse substances, which have hitherto resisted
all attempts at their analysis, and yet have a striking resem¬
blance, in natural characters, to the bodies with which they
are already associated ? For these reasons it appears to me,
that one arrangement is preferable to another, on no other
ground, than as it is better adapted for communicating a
knowledge of the subject; for all must be equally remote
from that perfection, which cannot be considered as attained,
till the science of chemistry shall no longer be capable of im¬
provement.
The order, which I have adopted as most eligible, is to
commence with those facts, which lead most directly to the
establishment of general principles. Attraction or affinity, as
the great cause of all chemical changes, and as admitting of
illustration by phenomena that are sufficiently familiar, has a
primary claim to consideration. Next to that of attraction,
the influence of Heat, over the forms and properties of bodies,
is the most generally observed fact ; and as heat is a power,
which is constantly opposed to that of affinity, there is the
more propriety in contrasting their operation. With heat,
Light also, as a repulsive agent, is frequently associated, and
Electricity belongs to the same class of powers. But as the
action of electricity consists, chiefly, in effecting the disunion
of chemical compounds, I have removed it from that place in
the system, which seems naturally to belong to it. For before
we can understand the general laws of electrochemical agency,
it is necessary to know something of oxygen and a few of the
inflammable bodies ; nor can the theory of the excitation of
INTRODUCTION.
XXXI
galvanic electricity be made at all intelligible, without this
previous knowledge.
The phenomena of heat, and the laws deduced from them,
conduct us naturally to the great source of that fluid, which
will be traced to a class of bodies agreeing, in mechanical
properties, writh the air of our atmosphere, and called airs or
gases. These gases, we shall find, consist partly of gravitating
matter, and partly of an extremely subtile fluid, which im¬
presses on our organs the sensation of heat, and is called
caloric When the ponderable ingredients, usually called
the bases , of these gases, combine together, or with other
bodies, caloric is given out, and newr compounds are generated.
It is on the possession or absence of the property of decom¬
posing one of them, oxygen gas, that a comprehensive division
has been made of bodies into combustible and incombustible .
In this view of the subject, combustion necessarily implies the
fixation of oxygen ; but the term has lately been extended to
every case of energetic chemical combination, which is accom¬
panied with heat and light. With oxygen, chlorine possesses
such numerous and close analogies, that it can only with pro¬
priety be placed along with that element, in the class of chemical
agents, which have been called supporters of combust ion. Iodine
is, also, entitled to the same rank ; and it is for purposes of
convenience, and with the view of giving a more complete his¬
tory of it, that I have placed it in a different part of the work.
The next division of bodies, that claim our attention, in¬
cludes those, which are formed either by the mixture or union
of the simple gases or of their bases. Thus oxygen and ni¬
trogen gases compose atmospheric air ; and hydrogen and
oxygen, water. Nitrogen and hydrogen, by their union,
afford ammonia ; and with this fluid the fixed alkalies are
naturally associated. The detail of properties belonging to
the alkalies and earths is, indeed, a necessary preliminary to
that of the acids, the most important quality of which is, that
they constitute, with the alkalies and earths, an extensive class
of neutral salts. The consideration of the bases of the alkalies
Light and electricity are probably, also, constituents of the gases.
XXX11
INTRODUCTION.
and earths has been made to follow that of the bodies them¬
selves, because these bases are the products of refined and
complicated operations, which could scarcely have been other¬
wise understood. The fixed alkalies, also, precede the volatile
ones, on account of the singular effects of potassium on am¬
monia.
The next class of compounds is that of Acids. With each
of these I have connected the history of its base, when known ;
for as several of these bodies have already lost, and others ap¬
pear likely to lose, their title to be considered as elementary,
it becomes merely a question of convenience where they
should be placed. In treating of the acids, their relation will
be traced to those bodies only which have already been de¬
scribed ; for it would be unseasonable to detail their action on
metals, till that class of substances has been specifically dis¬
cussed.
Having dismissed the consideration of such elementary
bodies, as are distinguished by affording acids when combined
with oxygen, of the properties of acids thus generated, and of
the compounds afforded by the union of acids with alkalies ; an
important division of elementary substances will next claim
our attention, viz. the Metals.
The class of bodies, it is usual to introduce at a much
earlier period: but I have adopted a different order, from the
consideration, that, with the previous knowledge of the con¬
stitution and qualities of acids, the history of the metals may
be made much more complete; and, especially, that all the
various modes and phenomena of their combination with
oxygen and chlorine may be more distinctly explained. The
more complex productions of the vegetable and animal king¬
doms will be the last step in our progress through the chemical
arrangement of bodies; and the concluding part of the work
will be occupied with practical rules, derived from the facts and
principles explained in the course of it, and applicable to the
solving of various interesting problems in chemical analysis.
ELEMENTS
OF
EXPERI MENTAL CH E MISTRY.
PART I.
CHAPTER I.
OF A CHEMICAL LABORATORY AND APPARATUS,
A CHEMICAL laboratory, though extremely useful, and
even essential, to all who embark extensively in the practice
of chemistry, either as an art, or as a branch of liberal know¬
ledge, is by no means required for the performance of those
simple experiments, which furnish the evidence of the funda¬
mental truths of the science. A room that is well lighted,
easily ventilated, and destitute of any valuable furniture, is
all that is absolutely necessary for the purpose. It is even ad-
viseable, that the construction of a regular laboratory should
be deferred, till the student has made some progress in the
science ; for he will then be better qualified to accommodate
its plan to his own peculiar views and convenience.
It is scarcely possible to offer the plan of a laboratory, which
will be suitable to every person, and to all situations ; or to
suggest any thing more than a few rules that should be gene¬
rally observed. Different apartments are required for the
various classes of chemical operations. The principal one
may be on the ground-floor; twenty-five feet long, fourteen
or sixteen wide, and open to the roof, in which there should
be contrivances for allowing the occasional escape of suffo¬
cating vapours. This will be destined chiefly for containing
furnaces, both fixed and portable. It should be amply fur¬
nished with shelves and drawers, and with a large table in the
VOL. I. B
CHEMICAL APPARATUS*
CHAP. I.
centre, the best form of which is that of a double cross.
Another apartment may be appropriated to the minuter ope¬
rations of chemistry; such as those of precipitation on a
small scale, the processes that require merely the heat of a
lamp, and experiments on the gases. In a third of smaller
size, may be deposited accurate balances, and other instru¬
ments of considerable nicety, which would be injured by the
acid fumes that are constantly spread through a laboratory.
The following are the principal instruments that are re¬
quired in chemical investigations; but it is impossible, with¬
out entering into very tedious details, to enumerate all the
apparatus that should be in the possession of a practical
chemist.
I. Furnaces. These may be formed either of solid brick¬
work, or of such materials as admit of their removal from
place to place.
The directions generally laid down in elementary books of
chemistry, for the construction of fixed furnaces, appear
to me deficient in precision, and such as a workman would
find it difficult to put in practice. I have, therefore, given
plans and sections, in the last two plates, of the various kinds
of furnaces ; and, in the Appendix, minute instructions will
be found for erecting them *.
The furnaces of most general utility are, 1st, the Wind
Furnace , in which an intense heat is capable of being excited
for the fusion of metals, &c. In this furnace, the body sub¬
mitted to the action of heat, or the vessel containing it, is
placed in contact with the burning fuel. Fig. 60 exhibits one
of the most common construction. Fig. 61 is the section of
a wind furnace ; the plan of which was obligingly communi¬
cated to me by Mr. Knight, of Foster-lane, London, to
whom, also, I am indebted for that represented, fig. 62.
The wind furnace of Mr. Chenevix is shown by fig. 74.
2dly, The Evaporating Furnace is formed of iron plates,
joined together by rabbiting, and placed over horizontal re¬
turning flues of brick. Figs. 64 and 65, are two views of this
* See the Description of the 7th and 8th plates in the Appendix.
CHAP. I.
CHEMICAL APPARATUS.
$
furnace as recommended by Mr. Knight. When evaporation
is performed by the naked fire, the vessel may be placed on
the top of the furnace, fig. 60 or 61 ; and when effected
through the intervention of a water bath, a shallow kettle of
water, in which is placed the evaporating dish and its con¬
tents, may be set in the same situation. For the purposes of
evaporating liquids, and drying precipitates on a small scale,
at a temperature not exceeding 212° Faff, a convenient appa¬
ratus is represented by fig. 27. 3dly, The plan of a Rever¬
beratory furnace is exhibited by figs. 66, 67, and 68. 4thly,
The Furnace far distilling by a Sand Heat is constructed by
setting upon the top of the brick-work, fig. 60, the iron pot,
fig. 71 ; a door being made in the side of the furnace for in-
troducing fuel. Distillation by the naked fire is performed
with the wind furnace, figs. 62, 63. 5thly, The Cupelling ,
or Enamelling Furnace , is shown by figs. 69, 70.
Portable furnaces, however, are amply sufficient for all the
purposes of the chemical student, at the outset of his pursuit.
The one which 1 prefer is that shown by figs. 58 and 59. It
was originally contrived, I believe, by Mr. Schmeisser * ; and
is made, with considerable improvements, and sold by Mr.
Knight, and by other dealers, in chemical apparatus. Its size
is so small, that it may be set on a table, and the smoke may
be conveyed by an iron pipe, into the chimney of the apart¬
ment. In the furnace, as it is usually sold, the chimney,
adapted for distillation with' a sand heat, passes directly
through the sand-bath, the form of which is necessarily
altered, from the common to a very inconvenient one. I
have found it a great improvement to make the aperture for
the chimney at k. This allows us to have a sand-bath of the
usual shape, as shown by fig. 59 ; or even to place evapo¬
rating dishes, or a small boiler, on the top of the furnace.
The aperture may be closed by a stopper, when we dispose
the furnace as shown by fig. 28. Dr. Black’s furnace is gene¬
rally made of a larger size, and is adapted to operations on a
more considerable scale. (See figs. 72 and 73.) Both these
furnaces are constructed of thin iron plates, and are lined
* See his Mineralogy, Tab. iii. and iv.
i CHEMICAL APPARATUS. CHAP. L
with fire-clay. They will be minutely described in the refer¬
ences to the plates.
For the purpose of exciting a sudden heat, and of raising
it to great intensity, nothing can be better adapted than a
very simple, cheap, and ingenious furnace, contrived by Mr.
Charles Aikin, fig. 55. It is formed out of pieces of black-
lead melting pots, in a manner to be described in the Ap¬
pendix, and is supplied with air by a pair of double bellows, d.
By a slight alteration, this furnace may occasionally be em¬
ployed for the operation of cupelling. (See fig. 57.)
II. For containing the materials, which are to be sub¬
mitted to the action of heat in a wind furnace, vessels called
crucibles are employed. They are most commonly made
of a mixture of fire clay and sand, occasionally with the ad¬
dition of plumbago, or black lead. The Hessian crucibles
are best adapted for supporting an intense heat without melt¬
ing; but they are liable to crack when suddenly heated or
cooled. The porcelain ones, made by Messrs. Wedgwood,
are of much purer materials, but are still more apt to crack
on sudden changes of temperature; and, when used, they
should, therefore, be placed in a common crucible of larger
size, the interval being filled with sand. The black-lead cru¬
cibles resist very sudden changes of temperature, and may be
repeatedly used ; but they are destroyed when some saline sub¬
stances (such as nitre) are melted in them, and are consumed
by a current of air. For certain purposes, crucibles are
formed of pure silver, or platina. Their form varies consi¬
derably, as will appear from inspecting plate vi. figs. 49, 50,
51, and 54. It is necessary, in all cases, to raise them from
the bars of the grate, by a stand, fig. 53, a or t. For the
purpose of submitting substances to the continued action of a
red heat, and with a considerable surface exposed to the air,
the hollow arched vessel, with a flat bottom, fig. 52, termed
a muffle, is commonly used. In fig. 69, d, e , the muffle is
shown, placed in a furnace for use.
III. Evaporating vessels should ahvays be of a flat shape,
so as to expose them extensively to the action of heat. (See
CHAP. I.
CHEMICAL APPARATUS
s
a section of one, fig. 12.) They are formed of glass, of
earthen ware, and of various metals. Those of glass are with
difficulty made sufficiently thin, and are often broken by
change of temperature ; but they have a great advantage in
the smoothness of their surface, and in resisting the action of
most acid and corrosive substances. Evaporating vessels of
porcelain, or Wedgwood’s ware, are next in utility, are less
costly, and less liable to be cracked. They are made both of
glazed and unglazed ware. For ordinary purposes the former
are to be preferred; but the unglazed should be employed
when great accuracy is required, since the glazing is acted
on by several chemical substances. Evaporating vessels of
glass, or porcelain, are generally bedded, up to their edge,
in sand (see fig. 65) ; but those of various metals are placed
immediately over the naked fire. When the glass or porcelain
vessel is very thin, and of small size, as a watch glass for ex¬
ample, it may be held by means of a small prong, represented
under fig. 12; or it may be safely placed on the ring of the
brass stand, plate i. fig. 13, and the flame of an Argand’s
lamp, cautiously regulated, may be applied beneath it. A
lamp thus supported, so as to be raised or lowered, at plea¬
sure, on an upright pillar, to which rings, of various diame¬
ters, are adapted, will be found extremely useful ; and, when
a strong heat is required, it is adviseable to employ a lamp,
furnished with double concentric wicks. A lamp for burn¬
ing spirit of wine will, also, be found very convenient, espe¬
cially if provided (as they now generally are) with a glass
cap to cover the wick when not in use, which, being
fitted by grinding, prevents the waste of the spirit by eva¬
poration.
IV. In the process of evaporation, the vapour for the most
part is allowed to escape; but of certain chemical processes,
the collection of the volatile portion is the principal object.
This process is termed distillation. It is performed in ves-
vels of various forms and materials. The common still is so
generally known, that a representation of it in the plates was
deemed unnecessary It consists of a vessel, generally of
* See Aikin’s Chem. Diet. pi. ii. fig. 31.
6
CHEMICAL APPARATUS.
CHAP. I.
copper, shaped like a tea-kettle, but without its spout and
handle. Into the opening of this vessel, instead of a common
lid, a hollow moveable head is affixed, which ends in a nar¬
row, open pipe. This pipe is received into another tube
of lead, which is twisted spirally, and fixed in a wooden tub,
so that it may be surrounded by cold water. (Fig. 40, del.)
When the apparatus is to be used, the liquid intended to be
distilled is poured into the body of the still, and the head is
fixed in its place, the pipe, which terminates it, being received
into the leaden worm. The liquid is raised into vapour, which
passes into the worm, is there condensed by the surrounding
cold water, and flows out at the lower extremity.
The common still, however, can only be employed for vola¬
tilizing substances that do not act on copper, or other metals,
and is, therefore, limited to very few operations. The vessel,
fig. 2, is of glass, or earthen ware, and is also intended for
distillation. It is termed an alembic , and consists of two parts;
the body a for containing the materials, and the head b by
which the vapour is condensed ; the pipe c conveying it to a
receiver. Vessels, termed retorts , however, are more generally
used. Fig. 1, a shows the common form, and fig. 13, a re¬
presents a stoppered, or tubulated retort. Retorts are made
of glass, of earthen ware, or of metal. When a liquid is to
be added at distant intervals during the process, the best con¬
trivance is that shown fig. 26, a, consisting of a bent tube,
with a funnel at the upper end. When the whole is intro¬
duced at first, it is done either through the tubulure, or, if
into a plain retort, through the funnel, fig. 10.
To the retort, a receiver is a necessary appendage; and this
may either be plain, fig. 1, b9 or tubulated, as shown by the
dotted lines at c. To some receivers a pipe is added (fig. 13, b),
which may enter partly into a bottle beneath. This vessel,
which is principally useful for enabling us to remove the dis¬
tilled liquid, at different periods of the process, is termed a
quilled receiver. For some purposes, it is expedient to have
the quilled part accurately ground to the neck of the bottle, c,
which would then be furnished with a tubulure, or second
neck, having a ground stopper, and should be provided, also,
with a bent tube, to be occasionally applied, for conveying
away any gases that may be produced. The condensation of
CHAP. I.
CHEMICAL APPARATUS.
1
the vapour is much facilitated, by lengthening the neck of the
retort with an adopter (fig. 11), the wider end of which slips
over the retort neck, while its narrow extremity is admitted
into the mouth of the receiver. (See fig. 63.)
Heat may be applied to the retort in several modes. When
the vessel is of earthen ware, and when the distilled substance
requires a strong heat to raise it into vapour, the naked fire is
applied, as shown fig. 63, Glass retorts are generally placed
in heated sand (fig. 59); and, when of a small size, the flame
of an Argand’s lamp, cautiously regulated, may be conve¬
niently used (fig. 13).
In several instances, the substance raised by distillation is
partly a condensable liquid, and partly a gas, which is not
condensed till it is brought into contact with water. To effect
this double purpose, a series of receivers, termed JVoulfe's
Apparatus , is employed. The first receiver (5, fig, 30) has a
right-angled glass tube, open at both ends, fixed into its tu-
bulure ; and the other extremity of the tube is made to ter-
minate beneath the surface of distilled water, contained, as
high as the horizontal dotted line, in the three-necked bottle
c. From another neck of this bottle, a second pipe proceeds,
which ends, like the first, under water, contained in a second
bottle d . To the central neck a straight tube, open at both
ends, is fixed, so that its lower end may be a little beneath
the surface of the liquid. Of these bottles any number may
be employed that is thought necessary.
The materials being introduced into the retort, the arrange¬
ment completed, and the joints secured in the manner to be
presently described, the distillation is begun. The condens¬
able vapour collects in a liquid form in the balloon b , while
the evolved gas passes through the bent pipe, beneath the sur¬
face of the water in c, which continues to absorb it till satu¬
rated. When the water of the .first bottle can absorb no
more, the gas passes, uncondensed, through the second right®
angled tube, into the water of the second bottle, which, in its
turn, becomes saturated. Any gas that may be produced,
which is not absorbable by wrater, escapes through the bent
tube e, and may be collected, if necessary.
Supposing the bottles to be destitute of the middle necks.
s
CHEMICAL APPARATUS.
CHAP. I.
and, consequently, without the perpendicular tubes, the pro¬
cess would be liable to be interrupted by an accident : for if,
in consequence of a diminished temperature, an absorption or
condensation of gas should take place, in the retort u, and, of
course, in the balloon 6, it must necessarily ensue that the
water of the bottles c and d would be forced, by the pressure
of the atmosphere, into the balloon, and possibly into the
retort; but, with the addition of the central tubes, a sufficient
quantity of air rushes through them to supply any .accidental
vacuum. This inconvenience, however, is still more con¬
veniently obviated by Welther’s tube of safety (fig. 31, b\
which supersedes the expediency of three-necked bottles. The
apparatus being adjusted, as shown by the figure, a small
quantity of water is poured into the funnel, so as to about
half fill the ball b. When any absorption happens, the fluid
rises in the ball, till none remains in the tube, when a quan¬
tity of air immediately rushes in. On the other hand, no gas
can escape, because any pressure from within is instantly fol¬
lowed by the formation of a high column of liquid in the per¬
pendicular part, which resists the egress of gas. This inge¬
nious invention I can recommend, from ample experience of
its utility*
Very useful alterations in the construction of Woulfe’s ap¬
paratus have been contrived also by Mr. Pepys and Mr.
Knight. That of the former is shown (fig. 32), where the
balloon b is surmounted by a vessel accurately ground to it,
and furnished with a glass valve, resembling that affixed to
Nooth’s apparatus. This valve allows gas to pass freely into
the vessel c, but prevents the water which it contains from
falling into the balloon. Mr. Knight’s improvement is de¬
scribed, and represented in a plate, in the Philosophical
Magazine, vol. xxf.
* Another modification of this apparatus, by Dr. Murray, is represented
in Nich. Journ. 8vo. vol. iih or in Murray’s System of Chemistry, vol. i.
pi. v. fig. 40. Fig. 41 of the same plate exhibits a cheap and simple form
of this apparatus, contrived by the late Dr. Hamilton, and depicted
originally in his translation of Berthollet on Dyeing. Mr. Burkitt’s im¬
provement of this apparatus may be seen in Nicholson’s Journal, 4to,
vol. v. 349.
CHAP. T.
CHEMICAL APPARATUS.
9
When a volatile substance is submitted to distillation, it is
necessary to prevent the escape of the vapour through the
junctures of the vessels; and this is accomplished by the ap¬
plication of lutes. The most simple method of confining the
vapour, it is obvious, would be to connect the places of junc¬
ture accurately together by grinding; and accordingly the
neck of the retort is sometimes ground to the mouth of the
receiver. This, however, adds too much to the expense of
apparatus to be generally practised.
When the distilled liquor has no corrosive property (such
as waiter, alcohol, ether, &c.), slips of moistened bladder, or
of paper, or linen, spread with flour paste, white of egg, or
mucilage of gum arabic, sufficiently answer the purpose. The
substance which remains, after expressing the oil from bitter
almonds, and which is sold under the name of almond-meal,
or powder, forms a useful lute, when mixed, to the consist¬
ency of glaziers’ putty, with water or mucilage. For confining
the vapour of acid, or highly corrosive substances, the fat lute
is well adapted, it is is formed by beating perfectly dry and
finely sifted tobacco pipe-clay, with painters’ drying oil, to
such a consistence that it may be moulded by the hand. The
same clay, beat up with as much sand as it will bear, without
losing its tenacity, with the addition of cut towT, or of horse-
dung, and a proper quantity of water, furnishes a good lute,
which has the advantage of resisting a considerable heat, and
is applicable in cases where the fat lute would be melted or
destroyed. Various other lutes are recommended by chemical
writers ; but the few that have been enumerated I find to be
amply sufficient for every purpose.
On some occasions, it is necessary to protect the retort from
too sudden changes of temperature, by a proper coating;. For
glass retorts, a mixture of moist common clay, or loam, with
sand, and cut shreds of tow or flax, may be employed. If
the distillation be performed by a sand heat, the coating needs
not to be applied higher than that part of the retort which is
bedded in sand ; but if the process be performed in a wind
furnace (fig. 63), the whole body of the retort, and that part
of the neck also which is exposed to heat, must be carefully
coated. To this kind of distillation, however, earthen retorts
2
10
CHEMICAL APPARATUS,
CHAP. I,
are better adapted ; and they may be covered with a compo¬
sition originally recommended by Mr. Willis. Two ounces
of borax are to be dissolved in a pint of boiling water, and a
sufficient quantity of slaked lime added, to give it the thick¬
ness of cream. This is to be applied by a painter’s brush,
and allowed to dry. Over this a thin paste is afterwards to be
applied, formed of slaked lime and common linseed-oil, well
mixed and perfectly plastic. In a day or two, the coating
will be sufficiently dry to allow the use of the retort.
For joining together the parts of iron vessels, used in distil¬
lation, a mixture of the finest China clay, with solution of
borax, is well adapted. In all cases, the different parts of any
apparatus made of iron should be accurately fitted by boring
and grinding, and the above lute is to be applied to the part
which is received into an aperture. This wall generally be
sufficient without any exterior luting : otherwise the lute of
clay, sand, and flax, already described, may be used.
In every instance, where a lute or coating is applied, it is
adviseable to allow it to dry before the distillation is begun ;
and even the fat lute, by exposure to the air during one or two
days after its application, is much improved in its quality.
The clay and sand lute is perfectly useless, except it be pre¬
viously quite dry. In applying a lute, the part immediately
over the juncture should swell outwards, and its diameter
should be gradually diminished on each side. (See fig. 13,
where the luting is shown, applied to the joining of the retort
and receiver.)
Beside the apparatus already described, a variety of vessels
and instruments are necessary, having little resemblance to
each other, in the purposes to which they are adapted. Glass
vessels are required for effecting solution , which often re¬
quires the application of heat, and sometimes for a consider¬
able duration. In the latter case, it is termed digestion, and
the vessel, fig. 4, called a matrass , is the most proper for per¬
forming it. When solution is required to be quickly effected,
the bottle, fig 5, with a rounded bottom, may be used ; or a
common Florence oil flask serves the same purpose extremely
well, and bears, without cracking, sudden changes of tempe-
CHAP. I®
CHEMICAL APPARATUS.
II
rature. For precipitations , and separating liquids from preci¬
pitates, the decanting-jar (fig. 14), will be found useful; or, if
preferred, it may be shaped as in fig. 26,/. Liquids, of dif¬
ferent specific gravities, are separated by the vessel, fig. 3 ; the
heavier fluid being drawn off through the cock b, and air
being admitted by the removal of the stopper a, to supply its
place. Glass rods, of various lengths, and spoons of the same
material, or of porcelain, are useful for stirring acid and cor¬
rosive liquids ; and a stock of cylindrical tubes, of various
sizes, is required for occasional purposes. It is necessary also
to be provided with a series of glass measures, graduated into
drachms, ounces, and pints. The small tube, fig. 15, called
a dropping tube , which is open at each end and blown in the
middle into a ball, will be found useful in directing a fine
stream of water upon the edges of a filtre, or any small ob¬
ject. The same purpose may, also, be very conveniently
effected by fixing a piece of glass tube of small bore, two or
three inches long, and bent at one end to an obtuse angle,
into a hole bored in a cork, which may be used as the stopple
of an eight ounce vial filled with water, fig. 25, a . On in¬
verting the vial, and grasping the bottom part of it, the warmth
of the hand expels either a few drops or a small stream of
water, which may be directed upon any minute object. When
the flow ceases, it may be renewed, if required, by setting the
bottle, for a moment, with its mouth upwards (which admits
a fresh supply of cool air), and then proceeding as before.
For the drying of precipitates, and other substances, by a
heat not exceeding 212°, a very useful apparatus is sold in
London. It is represented, supported by the ring of a lamp-
stand, by fig. 27. The vessel a is of sheet-iron or copper
japanned and hard-soldered ; c is a conical vessel of very thin
glass, having a rim, which prevents it, when in its place, from
entirely slipping into a; and cl is a moveable ring, which keeps
the vessel c in its place. When the apparatus is in use, water
is poured into a about as high as the dotted line ; the vessel c,
containing the substance to be dried, is immersed in the water,
and secured by the ring d ; and the whole apparatus set over
an Argand’s lamp. The steam escapes by means of the chim¬
ney 5, through which a little hot water may be occasionally
poured, to supply the waste by evaporation. By changing
12
CHEMICAL APPARATUS.
CHAP. I.
the shape of c to the segment of a sphere, still retaining the
rim, I have found it a most convenient vessel for evaporating
fluids.
Accurate beams and scales, of various sizes, with corres¬
ponding weights, some of which are capable of weighing seve¬
ral pounds, while the smaller size ascertains a minute fraction
of a grain, are essential instruments in the chemical labora¬
tory. So also are mortars of different materials, such as of
glass, porcelain, agate, and metal. Wooden stands, of various
kinds, for supporting receivers, should be provided * * * §. For
purposes of this sort, and for occasionally raising to a proper
height any article of apparatus, a series of blocks, made of
well seasoned wood, eight inches (or any other number) square,
and respectively eight, four, two, one, and half an inch in
thickness, will be found extremely useful ; since, by combining
them in different ways, thirty-one different heights may be
obtained.
The blow-pipe is an instrument of much utility in chemical
researches. A small one, invented by Mr. Pepys, with a flat
cylindrical box for condensing the vapour of the breath, and
for containing caps, to be occasionally applied with apertures
of various sizes, is perhaps the most commodious form t. One
of a much smaller size, for carrying in the pocket, has been
contrived by Dr. Wollaston J. A blow-pipe, which is sup¬
plied with air from a pair of double bellows, worked by the
foot §, may be applied to purposes that require both hands to
be left at liberty, and will be found useful in blowing glass,
and in bending tubes. The latter purpose, howrever, may be
accomplished by holding them over an Argand’s lamp with
double wicks. Occasionally, when an intense heat is required,
the flame of the blow-pipe, instead of being supported by the
mouth, may be kept up by a stream of oxygen gas, expelled
from a bladder or from a gas-holder |] . The blow-pipe
invented by Mr. Brooke consists of a small square box of
* See Aikin’s Cliem. Diet. pi. iv. fig. 59, e.
f See Aikin’s Chem. Diet. pi. vii. fig. 71, 72, 73.
J It is described in Nich. Journ. xv. 284.
§ Phil. Mag. xliii. 280.
jj See a representation of the apparatus for this purpose, in the Chemical
Conversations, pi. ix.
CHAP. I.
CHEMICAL APPARATUS.
15
copper or iron, into which air is forced by a condensing
syringe, and from which it is suffered to rush, through a tube
of very small aperture, regulated by a stop-cock, against the
flame of a lamp or candle #. By means of a screw added to
the syringe, the receiver may be filled with oxygen gas, or, as
will be described in chap. v. sect. 5, with a mixture of hy¬
drogen and oxygen gases. Blow-pipes on this construction
may be had of Mr. Newman, and of most of the other makers
of philosophical instruments.
In the course of this work, various other articles of appa¬
ratus will be enumerated, in detailing the purposes to which
they are adapted, and the principles on which they are con¬
structed. It must be remembered, however, that it is no part
of my object to describe every ingenious and complicated in¬
vention, which has been employed in the investigation of che¬
mical science: but merely to assist the student in attaining
apparatus for general and ordinary purposes. For such pur¬
poses, and even for the prosecution of new and important in¬
quiries, very simple means are sufficient; and some of the
most interesting chemical facts may be exhibited and even
ascertained, with the aid merely of Florence flasks, of com¬
mon vials, and of wine glasses. In converting these to the
purposes of apparatus, a considerable saving of expense will
accrue to the experimentalist; and he will avoid the encum¬
brance of various instruments, the value of which consists in
show, rather than in real utility.
In the selection of experiments, I shall generally choose
such as may be undertaken by persons not possessed of an
extensive chemical apparatus. On some occasions, however,
it may be necessary, in order to complete the series, that
others should be included, requiring, for their performance,
instruments of considerable nicety. The same experiment
may, perhaps, in a few instances, be repeatedly introduced in
illustration of different principles; but this repetition will be
avoided as much as possible. Each experiment will be pre¬
ceded by a brief enunciation of the general truth which it is
intended to illustrate.
* Thomson’s Annals, vii. 367 ; or, Journal of Science and the Arts, i.
u
CHAPTER II.
OF CHEMICAL AFFINITY.
All bodies, composing the material system of the universe,
have a mutual tendency to approach each other, whatsoever
may be the distances at which they are placed. The opera¬
tion of this force extends to the remotest parts of the planetary
system, and is one of the causes that preserve the regularity
of their orbits. The smaller bodies, also, that are under our
more immediate observation, are influenced by the same
power, and fall to the Earth’s surface, when not prevented
by the interference of other forces. From these facts, the
existence of a property has been inferred, which has been
called attraction , or more specifically, the attraction of gravita¬
tion. Its nature is entirely unknown to us ; but some of its
laws have been investigated, and successfully applied to the
explanation of phenomena. Of these, the most important are,
that the force of gravity acts on bodies directly in proportion
to the quantity of matter in each ; and that it decreases in the
reciprocal proportion of the squares of the distances.
From viewing bodies in the aggregate, we may next pro¬
ceed to contemplate them as composed of minute particles.
Of the nature of these particles, we have no satisfactory evi¬
dence. It is probable that they consist of solids, which are
incapable of mechanical division, but are still possessed of the
dimensions of length, breadth, and thickness. In simple
bodies, the particles must be all of the same nature, or homo¬
geneous. In compound bodies, we are to understand, by the
term, particles , the smallest parts into which bodies can be
resolved wfithout decomposition. The word atom has of late
been revived, to denote both these kinds of particles ; and we
may, therefore, speak with propriety of simple atoms and of
compound atoms . When two atoms of different kinds unite to
form a third or compound atom, we may term the two first
component atoms ; and if these have not been decomposed,
they may be called elementary or primary atoms.
CHAP. II. CHEMICAL AFFINITY, &C. IS
The atoms or particles of bodies are also influenced by the
force of attraction, but not unless when placed in apparent
contact. Hence a distinction has been made between gravita¬
tion, and that kind of attraction which is effective only at
insensible distances. The latter has been called contiguous
attraction or affinity ; and it has been distinguished, as it is
exerted between particles of matter, of the same kind, or be¬
tween particles of a different kind.
By the affinity of aggregation, the cohesive affinity , or, more
simply cohesion , is to be understood that force or power, by
which particles or atoms of matter of the same kind attract each
other, the only effect of this affinity being an aggregate or
mass. Thus a lump of copper may be considered as composed
of an infinite number of minute particles or integrant parts,
each of which has precisely the same properties, as those that
belong to the whole mass. These are united by the force of
cohesion. But if the copper be combined with another metal
(such as zinc), we obtain a compound (brass), the constituent
parts of which, copper and zinc, are combined by the power
of chemical affinity. In simple bodies, therefore, cohesion is
the only force exerted between their particles. But in com¬
pound bodies, we may distinguish the force, with which the
component atoms are united, from that which the compound
atoms exert towards each other: the former being united bv
chemical affinity, and the latter by the cohesive attraction.
SECTION I.
Of Cohesion , Solution , and Crystallization .
The cohesive affinity is a property, which is common to a
great variety of bodies. It is most strongly exerted in solids ;
and in these it is proportionate to the mechanical force re¬
quired for effecting their disunion. In liquids, it acts with
considerably less energy ; and in aeriform bodies we have no
evidence that it exists at all ; for their particles, as will after¬
wards be shown, are mutually repulsive, and, if hot held to-
6
16
CHEMICAL AFFINITY, &C.
CHAP. II.
gether by pressure, would probably separate to immeasurable
distances. Its force is not only different among different
bodies, but in various states of the same body. Thus in the
cohesion of certain metals (steel for instance), important
changes are produced by the rate of cooling, by hammering,
and by other mechanical operations. W ater, also, in a solid
state, has considerable cohesion, which is much diminished
when it becomes liquid, and is entirely destroyed when it is
changed into vapour.
The most important view, in which the chemist has to con¬
sider cohesion, is that of a force either counteracting; or modi-
fying chemical affinity; for the more strongly the particles of
any body are united by this power, the less are they disposed
to enter into combination with other bodies. In many cases,
a very powerful affinity existing between two substances may
be rendered wholly inefficient, by the strong cohesion of one
or both of them. Hence it has been received as an axiom,
that the affinity of composition is inversely proportionate to the
cohesive affinity. To the language, however, in which this
axiom is expressed, it has been justly objected, that it implies
an accuracy of proportion between the forces of cohesion and
of chemical affinity, which cannot be proved to exist; since
all that can truly be affirmed is, in general terms, that the
affinity of composition is less effective, as the attraction of
cohesion is stronger.
The cohesion of bodies may be overcome, 1st, by me¬
chanical operations, as by rasping, grinding, pulverising, and
other modes of division, which are generally employed as pre¬
liminary steps to chemical processes. In some instances, even
a minuter division of bodies is necessary, than can be accom¬
plished by mechanical means; and recourse is then had to
precipitation. Silica, for example, in the state of rock crystal,
may be boiled for a long time in liquid potash, without any
appearance of chemical action. It may even be bruised to the
finest powder, without being rendered sensibly soluble. But
when first precipitated from a state of chemical solution, it is
readily dissolved by that menstruum.
2dly. Cohesion may be counteracted by heat, applied so as
to melt one or both of the bodies, if fusible; or to raise them
*
SECT. I.
CHEMICAL AFFINITY, &C.
17
into vapour, if volatile. Lead and sulphur contract no union,
till one or both of them is melted by heat. Arsenic and sul¬
phur are united most effectually, by bringing them into con¬
tact, when both are in a state of vapour.
3dly. Cohesion may be counteracted by solution ; and this
is so general a condition of chemical: union, that it was
formerly received as an axiom, that bodies do not act on each
other , unless one or both are in a state of solution ; a principle,
to which the progress of chemical science has since discovered
many exceptions.
The term solution is applied to a very extensive class of phe¬
nomena. When a solid disappears in a liquid, or when a solid
or liquid is taken up by an aeriform body, if the compound
exhibit perfect transparency, we have, in each instance, an
example of solution. The expression is applied, both to the
act of combination, and to the result of the process. When
common salt, such as is used in cookery, is agitated with
water, it disappears ; in other words, its solution takes place ;
and we also term the liquid which is obtained, a solution of
salt in water. This is one of the simplest cases that can be
adduced, of the efficiency of chemical affinity ; for solution is
always the result of an affinity between the fluid and the solid
which is acted upon, sufficient in force to overcome the co¬
hesion of the solid. This affinity continues to act, until, at
length, a certain point is attained, where the affinity of the
solid and fluid for each other is overbalanced by the cohesion
of the solid, and the solution cannot be carried farther. This
point is called saturation , and the fluid obtained is termed a
saturated solution .
With respect to common salt, water acquires no increase
of its solvent power by the application of heat. But there
are various salts with which water may be saturated at the
common temperature of the atmosphere, and will yet be '
capable of dissolving a still farther quantity by an increase of
its temperature. When a solution, thus charged with an ad¬
ditional quantity of salt, is allowed to cool, the second portion
of salt is deposited in a form resembling its original one.
To recover a salt from its solution, if its solubility does not
vary with the temperature of the solvent, as in the instance
VOL. i. c
CHEMICAL AFFINITY, &C.
CHAP. II,
II
of common salt, it is necessary to expel a portion of the fluid
by heat. This constitutes the process of evaporation. II the
evaporation be carried on very slowly, so that the particles oi
the solid may approach each other in the way best adapted to
them, we obtain solid figures, of a regular shape, called crys¬
tals . The crystallization of a solid may also take place from
that state of fluidity which is produced by heat. Thus several
of the metals crystallize on cooling from a melted state ; and
some volatile bodies, as arsenic, assume, when condensed from
the state of vapour, the shape of regular crystals.
In the act of separating from the water in which they were
dissolved, the crystals of almost all salts carry with them a
quantity of water, which is essential to the regularity of their
form, and cannot be expelled without reducing them to shape¬
less masses. It is termed their water of crystallization. Its
proportion varies in different salts; in some it is extremely
small ; in others it constitutes the principal part of the salt,
and is even so abundant, as to liquefy them on the applica¬
tion of heat, producing what is called the watery fusion. The
water of crystallization is retained also in different salts with
very different degrees of force. Some crystals, which lose
their watery ingredient by mere exposure to the atmosphere,
are said to effloresce. Others, on the contrary, not only hold
their water of crystallization very strongly, but even attract
more; and, on exposure to the atmosphere, become liquid,
or deliquiate. The property itself is called deliquescence .
When two salts are contained in the same solution, which
vary, in their degree of solubility, and which have no remark¬
able attraction for each other, they may be obtained separate.
For by carefully reducing the quantity of the solvent by eva¬
poration, the salt whose particles have the greatest cohesion,
will crystallize first. If both salts are more soluble in hot
than in cold water, the crystals will not appear till the liquid
cools. But if one of them, like common salt, is equally solu¬
ble in hot and in cold water, crystals will appear, even during
the act of evaporation. In this way we may completely sepa¬
rate nitre from common salt, the crystals of the latter being
formed during evaporation ; while those of nitre do not appear
till some time after the fluid has cooled.
SECT* I. ' CHEMICAL AFFINITY, &C. 19
Salts, which are thus deposited in regular shapes, generally
adhere to the surface of the vessel containing the solution, or
to any substance, such as pieces of thread or of wood, intro¬
duced for the purpose of collecting them. But a still more
effectual way of inducing crystallization is to immerse, in the
solution, a crystal of the same kind with that which we expect
to be formed. The crystal, thus exposed, receives successive
additions to its several surfaces, and preserves its form, with
a considerable addition to its magnitude. This curious fact
was originally noticed by Le Blanc, who has founded on it a
method of obtaining large and perfect crystals.
In some instances, the affinity of a salt for its solvent is so
powerful, that it will not separate from it in the form of crys¬
tals; but will yet crystallize from another fluid, which is
capable of dissolving it, and for which it has a weaker affinity.
Pot-ash, for instance, cannot be made to crystallize from its
watery solution, but will yet separate, in a regular form, from
its solution in alcohol.
Every solid, that is susceptible of crystallization, has a
tendency to assume a peculiar shape. Thus common salt,
when most perfectly crystallized, forms regular cubes ; nitre
has the shape of a six-sided prism ; and alum that of an oc¬
tahedron. It has, indeed, been alleged, as an objection to the
modern theory of crystallization, that minerals, differing essen¬
tially in their composition, have precisely the same primitive
form. For example, the primitive form of carbonate of lime,
and of the compound carbonate of lime and magnesia, is, in
both, a regular rhomboid, so nearly resembling each other,
as to have been supposed to be precisely the same. In this
case, however, Dr. Wollaston has shown, that though the
figures are similar, yet their angles, on admeasurement by a
nice instrument, differ very appreciably*. But other instances
have been since brought forward by M. Beudant, in which
artifical salts, composed of dissimilar ingredients, have the same
crystalline form ; and Dr. Wollaston has satisfied himself of
the accuracy of M. Beudant’s remark, that the mixed sul¬
phates of copper and iron, of zinc and iron, and of copper
* Phil. Trans. 1812.
c 2
25
CHEMICAL AFFINITY, &C.
CHAP. II.
zinc and iron, assume forms, in which no difference has yet
been discovered from that of simple sulphate of iron alone*.
He apprehends, indeed, that on minute investigation, some
difference will be found, either in the angles or linear measures
of those different salts ; but till this has been established, the
facts, as they stand, must be acknowledged to be exceptions
to the principle, that identity of crystalline form is necessarily
connected with identity of chemical composition. In the instances
which have been given, the perfect transparency of the crys¬
tals forbids our considering them as an intermixture of foreign
matter grouped together by sulphate of iron ; and this expla¬
nation is, also, irreconcileable with the fact, discovered by
Dr. Wollaston, that a mixed solution of sulphates of zinc and
copper, in certain proportions, affords crystals which, though
containing no iron, still agree so nearly in form with those of
sulphate of iron, that he could not undertake to point out
any difference between them.
It has been long known that the same solid admits of great
varieties of crystalline figure, without any variation of its che¬
mical composition. Calcareous spar, for example, appears in
six-sided prisms, in three or six-sided pyramids, anti in many
other shapes. These varieties are occasioned by accidental cir¬
cumstances, which modify the operation of the force of cohe¬
sion. The diversities of shape are, on first view, extremely
numerous ; and yet, upon a careful examination and compari¬
son, they are found to be reducible to a small number of simple
figures, which, for each individual species, is always the same.
The attempt to trace all the observed forms of crystals to
a few simple or primary ones, seems to have originated with
Bergman f. In the instance of calcareous spar, this distin¬
guished chemist demonstrated that its numerous modifications
may possibly result from one simple figure, the rhomb, by
the accumulation of which, in various ways, crystals of the
most opposite forms may be generated. This theory he ex¬
tended to crystals of every kind; and he accounted for the
differences of their external figures, by varieties of their me¬
chanical elements or minute molecules.
* Thomson's Annals, xi. 262, 283.
f Bergman's Essays, ii.
SECT. I.
CHEMICAL AFFINITY, &C.
n
About the same period with Bergman, or immediately
afterwards, M. Rome de l’Isle pursued still farther the theory
of the structure of crystals. He reduced the study of crystal-
lography to principles more exact, and more consistent with
observation. He classed together, as much as he was able,
crystals of the same nature. From among the different forms
belonging to the same species, he selected, for the primitive
form, one which appeared to him to be the most proper, on
account of its simplicity. Supposing this to be truncated in
different manners, he deduced the other forms, and established
a certain gradation, or series of passages, from the primitive
form to complicated figures, which on first view would scarcely
appear to have any connexion with it. To the descriptions
and figures of the primitive forms, he added the mechanical
measurement of the principal angles, and showed that these
angles are constantly the same in each variety. It must be
acknowledged, however, that the primitive forms, assumed by
this philosopher, were entirely imaginary, and not the result
of any experimental analysis. His method was to frame an
hypothesis ; and then to examine its coincidence with actual
appearances. On his principles any form might have been
the primitive one, and any other have been deduced from it.
It was reserved for the sagacity of the Abbe Haiiy to unfold
the true theory of the structure of crystals, and to support it
both by experimental and mathematical evidence. By the
mechanical division of a complicated crystal, he first obtains
the simple form, and afterwards constructs, by the varied ac¬
cumulation of the primitive figure, according to mathematical
synthesis, all the observed varieties of that species.
Every crystal may be divided by means of proper instru¬
ments ; and, if split in certain directions, presents plane and
smooth surfaces. If split in other directions, the fracture is
rugged, is the mere effect of violence, and is not guided by
the natural joining of the crystal. This fact had been long
known to jewellers and lapidaries; and an accidental obser¬
vation of it proved, to the Abbe Haiiy, the key of the whole
theory of crystallization. By the skilful division of a six-
sided prism of calcareous spar, he reduced it to a rhomb, pre¬
cisely resembling that which is known under the name of Ice-
22
CHEMICAL AFFINITY, &C.
CHAP. II.
land crystal. Other forms of calcareous spar were subjected
to the same operation ; and, however different at the outset,
finally agreed in yielding, as the last product, a rhomboidal
solid. It was discovered also by Haiiy, that if we take a
crystal of another kind (the cubic fluor spar for instance), the
nucleus, obtained by its mechanical division, will have a dif¬
ferent figure, viz. an octahedron. Other crystallized bodies
produce still different forms ; which are not, however, very
numerous. Those which have hitherto been discovered, are
reducible to six ; the parallelopipedon, which includes the
cube, the rhomb, and all the solids which are terminated by
six faces, parallel two and two ; the tetrahedron ; the octahe¬
dron ; the regular hexaliedral prism ; the dodecahedron with
equal and similar rhomboidal planes ; and the dodecahedron
with triangular planes.
The solid of the primitive form or, nucleus of a crystal ob¬
tained by mechanical division, may be subdivided in a direc¬
tion parallel to its different faces. All the sections thus pro¬
duced being similar, the resulting solids are precisely similar
in shape to the nucleus, and differ from it only in size, which
continues to decrease as the division is carried farther. To
this division, however, there must be a limit, beyond which
we should come to particles so small, that they could no lon¬
ger be divided. At this term, therefore, wre must stop : and
to these last particles, the result of an analysis of the primitive
nucleus, and similar to it in shape, Haiiy has given the name
of the integrant molecule. If the division of the nucleus can
be carried on in other directions than parallel to its faces, the
integral molecule may then have a figure different from that
of the nucleus. The forms, however, of the integrant mole¬
cule, which have hitherto been discovered, are only three ; the
tetrahedron, the simplest of pyramids ; the triangular prism,
the simplest of prisms ; and the parallelopipedon, including
the cube and rhomboid, the simplest of solids which have
their faces parallel two and two. With respect to octahedral
crystals, there is a difficulty, whether the octahedron, or
tetrahedron, is to be adopted as the primitive form ; and,
whichsoever be chosen, since neither of them can fill space
without leaving vacuities, it is not easy to conceive any ar-*
Sfi€T f.
CHEMICAL AFFINITY, &C.
2S
rangement, by which the particles will remain at rest. To
obviate this difficulty, Dr. Wollaston has suggested that, in
such instances, the elementary particles may be perfect
spheres ; and by the due application of spheres to each other?
he has shown, that a variety of crystalline forms may be pro¬
duced*; viz. the octohedron, the tetrahedron, and the acute
rhomboid. If other particles, having the same relative ar¬
rangement, be supposed to have the shape of oblate spheroids,
the regular rhomboid will be the resulting figure ; 'and if the
spheroids be oblong instead of oblate, they will generate prisms
of three or six sides. The cube, also, Dr. Wollaston has
shown, may be explained by the aggregation of spheroidical
particles.
A method of developing the structure of crystals, by a new
process, which appears greatly superior to that of mechanical
divisions, has been lately described by Mr. Daniel f. It con¬
sists in exposing any moderately soluble salt to the slow and
regulated action of a solvent. A shapeless mass of alum, for
instance, weighing about 1500 grains, being immersed in 15
ounce measures of water, and set by, in a quiet place, for
a period of three or four weeks, will be found to have
been more dissolved toward the upper than the lower part,
and to have assumed a pyramidal form. On further exa¬
mination, the lower end of the mass will present the form
of octahedrons and sections of octahedrons, in high relief and
of various dimensions. They will be most distinct at its
lower extremity, becoming less so as they ascend. This new
process of dissection admits of exclusive application. Borax,
in the course of six weeks, exhibits eight sided prisms with
various terminations; and other salts may be made to un¬
fold their external structure by the slow agency of water. Car¬
bonate of lime, carbonate of strontites, and carbonate of
barytes, give also distinct results, when acted upon by weak
acids; and even amorphous masses of those metals, which
have a tendency to assume a crystalline form, such as bismuth,
antimony, and nickel, when exposed to very dilute nitric acid,
presented at the end of a few days distinct crystalline forms.
The results of these experiments, when minutely traced and
* PhiL Trans. 1813, p. 51. + Jour, of Science and the Arts, i. 94.
24?
CHEMICAL AFFINITY, &C.
CHAP. II.
investigated, as has been ably done in Mr. Daniel’s Memoir,
afford strong confirmation to the theory, that the spheroidical
is the true form of the ultimate particles of crystallized bodies.
The primitive form, and that of the integral molecule hav¬
ing been experimentally determined by the dissection of a
crystal, the next step is to discover the law, acording to which
these molecules are arranged, in order to produce, by their
accumulation around the primitive figure, the great variety of
secondary forms. What is most important in the discoveries
of Haiiy, and what constitutes in fact the essence of his theory,
is the determination of these laws, and the precise measure¬
ment of their action. Fie has shown that all the parts of a
secondary crystal, superadded to the primitive nucleus, con¬
sist of laminae, which decrease gradually by the subtraction
of one or more layers of integrant molecules; so that theory
is capable of determining the number of these ranges, and,
by a necessary consequence, the exact form of the secondary
crystal.
By the developement of these laws of decrement, Haiiy
has shown how, from variations of the arrangement of the
integrant molecules, a great variety of secondary figures may
be produced. Their explanation, however, would involve a
minuteness of detail, altogether unsuitable to the purpose of
this work ; and I refer, therefore, for a very perspicuous state¬
ment of them, to the first and ninth volumes of the Philoso¬
phical Magazine.
SECTION II.
Of Chemical Affinity , and the General Phenomena of Chemical
Action .
Chemical affinity, like the cohesive attraction, is effective
only at insensible distances ; but it is distinguished from the
latter force, in being exerted between the particles or atoms of
bodies of different kinds. The result of its action is not a
mere aggregate, having the same properties as the separate
parts, and differing only by its greater quantity or mass, but
a new compound, in which the properties of the components
have either entirely or partly disappeared, and in which new
SECT II.
CHEMICAL AFFINITY, &C.
25
qualities are also apparent. The combinations effected by
chemical affinity are permanent, and are destroyed only by the
interference of a more powerful force, either of the same or of
a different kind.
As a general exemplification of chemical action, we may
assume that which takes place between potash and sulphuric
acid. In their separate state, each of these bodies is distin¬
guished by striking peculiarities of taste, and by other quali¬
ties. The alkali, on being added to blue vegetable infusions,
changes their colour to green ; and the acid turns them red.
But if wre add the one substance to the other, very cautiously
and in small quantities, examining the effect of each addition,
we shall at length attain a certain point, at which the liquid
will possess neither acid nor alkaline qualities ; the taste will
be converted into a bitter one ; and the mixture will produce
no effect on blue vegetable colours. Here then, the qualities
of the constituent parts, or at least some of their most im¬
portant ones, are destroyed by combination. When opposing
properties thus disappear, the bodies combined have been
said to saturate each other ; and the precise term, at which
this takes place, has been called the point of saturation. It is
adviseable, however, to restrict this expression to weaker com¬
binations, where there is no remarkable alteration of qualities,
as in cases of solution ; and to apply to those results of more
energetic affinities, which are attended with Joss of properties,
the term neutralization .
At the same time that the properties of bodies disappear on
combination, other new qualities, both sensible and chemical,
are acquired ; and the affinities of the components for other
substances become in some cases increased, in others dimi¬
nished in energy. Sulphur, for example, is destitute of taste,
smell, or action on vegetable colours ; and oxygen gas is, in
these respects, equally inefficient. But the compound of sul¬
phur and oxygen is intensely acid ; the minutest portion in¬
stantly reddens blue vegetable infusions; and the acid is dis¬
posed to enter into combination with a variety of bodies, for
which its components evinced no affinity. Facts of this kind
sufficiently refute the opinion of the older chemists, that the
properties of compounds are intermediate between those of their
tQ CHEMICAL AFFINITY, &C. CHAP. II.
f
component parts; for, in instances like the foregoing, the
compound has qualities, not a vestige of which can be traced
to either of its elements.
It is not, however, in all cases, that the change of properties
is so distinct and appreciable by the senses, as in the instances
which have been just now described. In some examples of
chemical union, the change is scarcely perceptible to the eye
or taste, when the chemist is nevertheless certain that combi¬
nation must have taken place. This occurs chiefly in the
mixture of saline solutions with each other, where a complete
exchange of principles ensues, without any evident change of
properties. Examples of this kind cannot, however, be un¬
derstood, till the subject of complex affinity has been first elu¬
cidated .
The existence of chemical affinity between any two bodies
is inferred, therefore, from their entering into chemical com¬
bination ; and that this has happened, a change of properties
may be considered as a sufficient proof, even though the
change may not be very obvious, and may require accurate
examination to be perceived at all.
The proof, which establishes the nature of chemical com¬
pounds, is of two kinds, synthesis and analysis . Synthesis
consists in effecting the chemical union of two or more bodies ;
and analysis in separating them from each other, and exhibit¬
ing them in a separate state. When we have a compound of
two or more ingredients, which are themselves compounded
also, the separation of the compounds from each other may
be called the proximate analysis of the body ; and the farther
separation of these compounds into their most simple prin¬
ciples, its ultimate analysis . Thus the proximate analysis of
sulphate of potash consists in resolving it into potash and sul¬
phuric acid ; and its ultimate analysis is effected by decom¬
posing the potash into potassium and oxygen, and the sul¬
phuric acid into oxygen and sulphur.
When the analysis of any substance has been carried as far
as possible, we arrive at its most simple principles, or elements ,
by which expression we are to understand, not a body that is
incapable of further decomposition, but only one which has
not yet been decomposed . The progress of chemical science.
SECT. IT.
CHEMICAL AFFINITY, &C.
27
for several centuries past, lias consisted in carrying still farther
the analysis of bodies, and in proving those to be com¬
pounded, which had before been considered as elementary.
Beside the alteration of properties, which usually accom¬
panies chemical action, there are certain other phenomena,
which are generally observed to attend it.
1st. In almost every instance of chemical union, the specific
gravity of the compound is greater than might have been in¬
ferred from that of its components; and this is true both
of weaker and more energetic combinations. When equal
weights of water and sulphuric acid are made to combine, the
specific gravity of the resulting liquid is not the mean, but
considerably greater than the mean. The law extends also
to solids. But though general, it is not universal ; for in a
very few instances, chiefly of aeriform fluids, condensation
does not attend chemical union. And in the combination of
metals with each other the reverse even takes place, the com¬
pound being specifically lighter than might have been ex¬
pected, from the specific gravity of its elements, and their
proportion to each other.
2dly. When bodies combine chemically, it may be received
as a general fact, that their temperature changes. Equal
weights of oil of vitriol and water, both at the temperature of
50° of Fald., are heated, by sudden mixture, to considerably
above 212°. In other examples, a contrary effect takes place,
and a diminished temperature, or, in other words, a produc¬
tion of cold, is observed. This is all that it is at present
necessary to state on the subject, which will be more fully
considered when we come to treat of caloric.
3dly. The forms of bodies are often materially changed by
chemical combination. Two solids may, by their union, be¬
come fluid ; or two fluids may become solid. Solids are also
often changed into aeriform fluids; and, in many instances,
the union of two airs, or gases, is attended with their sudden
conversion into the solid state. By long exposure of quick¬
silver to a moderate heat, we change it from a brilliant liquid
into a reddish scaly solid ; and by heating this solid in a re¬
tort, we obtain an aeriform fluid, or gas, in considerable
quantity, and recover the quicksilver in its original form.
6
28
CHEMICAL AFFINITY, &C.
CHAP. II.
4thly. Change of colour is a frequent, but not universal
concomitant of chemical action. In some cases, brilliant
colours are destroyed, as when oxymuriatic acid is made to
act on solution of indigo. In other instances, two substances,
which are nearly colourless, form, by their union, a com¬
pound distinguished by beauty of colour, as when liquid pot¬
ash is added to a very dilute syrup of violets. Certain colours
appear also to belong essentially to chemical compounds, and
to be characteristic of them. Thus 100 parts of quicksilver,
and 4 of oxygen, invariably give a black compound; and the
same quantity, with 8 parts of oxygen, a red compound.
SECTION III.
Of the Proportions in which bodies combine ; and of the Atomic
In the chemical combination of bodies with each other, a
few leading circumstances deserve to be remarked.
1st. Some bodies unite in all proportions; for example,
water and sulphuric acid, or water and alcohol.
2dly. Other bodies combine in all proportions, as far as a
certain point, beyond which combination no longer takes
place. Thus water will take up successive portions of com¬
mon salt, until at length it becomes incapable of dissolving
any more. In cases of this sort, as well as in those included
under the first head, combination is wreak and easily destroyed,
and the qualities wdiich belonged to the components in their
separate state continue to be apparent in the compound.
3dly. There are many examples in which bodies unite in
one proportion only ; and in all such cases the proportion of
the elements of a compound must be uniform for the species.
Thus hydrogen and oxygen unite in no other proportions,
than those constituting water, which, by weight, are very
nearly 11 a of the former to 88A of the latter, or 1 to 7 a* In.
cases of this sort, the combination is generally energetic ; and
the characteristic qualities of the components are no longer
observable in the compound.
SECT. III. CHEMICAL AFFINITY, &C. 29
4thly. Other bodies unite in several proportions : but these
proportions are definite, and, in the intermediate ones, no
combination ensues. Thus 100 parts by weight of charcoal
combine with 1324- of oxygen, or with 2 65, but with no in¬
termediate quantity; 100 parts of manganese combine with
14 of oxygen, or with 28, or with 42, or with 56, and with
those proportions only.
Now it is remarkable, that when one body enters into com¬
bination with another, in several different proportions, the
numbers indicating the greater proportions are exact simple
multiples of that denoting the smallest proportion. In other
words, if the smallest proportion in which B combines with A,
be denoted by 10, A may combine with twice 10 of B, or
with three times 10, and so on; but with no intermediate
quantities. There cannot be a more striking instance of this
law than that above mentioned, of the compounds of manga¬
nese with oxygen ; in which the oxygen of the three last
compounds may be observed to be a multiplication of that of
the first (14) by the numbers 2, 3, and 4. Examples, in¬
deed, of this kind have, of late, so much increased in number,
that the law of simple multiples bids fair to become universal,
with respect at least to chemical compounds, the proportions
of which are definite.
Facts of this kind are not only important in themselves,
but also on account of the generalizations that have been de¬
duced from them ; for on them Mr. Dalton has founded what
may be termed the Atomic Theory of the chemical Constitution
of Bodies. Till this theory was proposed, we had no adequate
explanation of the uniformity of the proportions of chemical
compounds ; or of the nature of the cause which renders,
combination, in other proportions, impossible. In this place
I shall offer only a brief illustration of the theory ; for in the
course of the work I shall have occasion to apply it to the
explanation of a variety of phenomena.
Though we appear, when wre effect the chemical union of
bodies, to operate on masses , yet it is consistent with the most
rational view of the constitution of bodies to believe, that it
is only between their ultimate particles , or atoms , that combi¬
nation takes place.. By the term atoms , it has been already
30
CHEMICAL AFFINITY, &C.
CHAP. II,
stated, we are to understand the smallest parts of which bodies
are composed. An atom, therefore, must be mechanically
indivisible, and of course a fraction of an atom cannot exist.
Whether the atoms of different bodies be of the same size, or
of different sizes, we have no sufficient evidence. The pro¬
bability is, that the atoms of different bodies are of unequal
sizes ; but it cannot be determined whether their sizes bear
any regular proportion to their weights. We are equally
ignorant of their shape; but it is probable, though not essen¬
tial to the theory, that they are spherical. This, however,
requires a little qualification. The atoms of all bodies pro¬
bably consist of a solid corpuscle, forming a nucleus, and of
an atmosphere of heat, by which that corpuscle is surrounded ;
for absolute contact is never supposed to take place between
the atoms of bodies. The figure of a simple atom may rea¬
dily, therefore, be conceived to be spherical. But in com¬
pound atoms, consisting of a single central atom, surrounded
by other atoms of a different kind, it is obvious that the
figure (contemplating the solid corpuscles only) cannot be
spherical ; yet if we include the atmosphere of heat, the figure
of a compound atom may be spherical, or some shape ap¬
proaching to a sphere.
Taking for granted that combination takes place between
the atoms of bodies only, Mr. Dalton has deduced, from the
relative weights in which bodies unite, the relative weights of
their ultimate particles, or atoms. When only one combina¬
tion of any two elementary bodies exists, he assumes, unless
the contrary can be proved, that its elements are united atom
to atom singly. Combinations of this sort he calls binary .
But if several compounds can be obtained from the same ele¬
ments, they combine, he supposes, in proportions expressed
by some simple multiple of the number of atoms. T he fol¬
lowing table exhibits a view of some of these combinations :
1 atom of A + 1 atom of B = 1 atom of C, binary.
1 atom of A + 2 atoms of B = 1 atom of D, ternary.
2 atoms of A + 1 atom of B = 1 atom of E, ternary.
1 atom of A + 3 atoms of B = 1 atom of F, quaternary.
3 atoms of A 4- 1 atom of B = 1 atom of G, quaternary.
SECT. III.
CHEMICAL AFFINITY, &C.
31
A different classification of atoms has been proposed by
Berzelius, viz. into, Istly, elementary atoms ; 2dly, compound
atoms. The compound atoms he divides again into three
different species, namely, 1st, atoms formed of only two ele¬
mentary substances united, or compound atoms of the first order:
2dly, atoms composed of more than two elementary substances;
and these, as they are only found in organic bodies, or bodies
obtained by the destruction of organic matter, he calls organic
atoms : Sdly, atoms formed by the union of two or more com¬
pound atoms; as for example, the salts. These he calls com -
pound atoms of the second order .
If elementary atoms of different kinds were of the same
size, the greatest number of the atoms of A that could be com¬
bined with an atom of B would be 1 2 ; for this is the greatest
number of spherical bodies that can be arranged in contact
with a sphere of the same diameter. But this equality of size,
though adopted by Berzelius, is not necessary to the hypo¬
thesis of Mr. Dalton ; and is, indeed, supposed by him not
to exist.
As an illustration of the mode in which the weight of the
atoms of bodies is determined, let us suppose that any two
elementary substances, A and B, form a binary compound ;
and that they have been proved experimentally to unite in the
proportion, by weight, of 5 of the former to 4 of the latter ;
then, since, according to the hypothesis, they unite particle
to particle, those numbers will express the relative weights of
their atoms. But besides combining atom to atom singly,
1 atom of A may combine with 2 of B, or with 3, 4, &c. Or
1 atom of B may unite with 2 of A, or with 3, 4, &c. When
such a series of compounds exists, the relative proportion of
their elements ought necessarily, on analysis, to be proved to be
5 of A to 4 of B ; or 5 to (4 -f 4 = ) 8 ; or 5 to (4 + 4 + 4 =)
12, &c. ; or, contrariwise, 4 of B to 5 of A ; or 4 to (5 4- 5 = )
10; or 4 to (5 -f 5 *f 5 = ) 15. Between these there ought
to be no intermediate compounds ; and the existence of any
such (as 5 of A to 6 of B, or 4 of B to If of A) would, if
clearly established, militate against the hypothesis.
To verify these numbers, it may be proper to examine the
CHEMICAL AFFINITY, &C.
CHAP. II.
QQ
xJ JLi
combinations of A and B with some third substance, for ex¬
ample with C. Let us suppose that A and 0 form a binary
compound, in which analysis discovers 5 parts of A and 3 of C.
Then, if C and B are, also, capable of forming a binary com¬
pound, the relative proportion of its elements ought to be 4 of
B to 3 of C ; for these numbers denote the relative weights of
their atoms. Now this is precisely the method, by which Mr.
Dalton has deduced the relative weights of oxygen, hydrogen,
and nitrogen ; the two first from the known composition of
water, and the two last from the proportion of the elements
of ammonia. Extending the comparison to a variety of other
bodies, he has obtained a scale of the relative weights of their
atoms.
In several instances, additional evidence is acquired of the
accuracy of the weight, assigned to an element, by our ob¬
taining the same number from the investigation of several of
its compounds. For example:
1. In water , the hydrogen is to the oxgen as 1 to 7*5.
2. In olejiant gas , the hydrogen is to the carbon as 1 to 5*65.
3. In carbonic oxide the oxygen is to the carbon as 7*5 to 5'(i5.
Whether, therefore, we determine the weight of the atom
of carbon, from the proportion in which it combines with
hyd rogen, or with oxygen, we arrive at the same number 5*65;
an agreement which, as it occurs in various other instances,
can scarcely be an accidental coincidence. In a similar man¬
ner, 7*5 is declucible, as representing the atom of oxygen,
both from the combination of that base with hydrogen and
with carbon; and 1 is inferred to be the relative weight of
the atom of hydrogen from the two principal compounds into
which it enters.
In selecting the body, w7hich should be assumed as unity,
Mr. Dalton has been induced to fix on hydrogen, because it
is that body which unites with others in the smallest propor¬
tion. Thus, in water, we have 1 of hydrogen by weight to
7~ of oxygen in ammonia, 1 of hydrogen to 5 of nitrogen ;
in carbureted hydrogen, 1 of hydrogen to 5*65 of carbon ;
and in sulphureted hydrogen, 1 of hydrogen to 15 of sulphur.
SECT. III.
CHEMICAL AFFINITY, &C.
ss
Taking for granted that all these bodies are binary compounds,
we have the following scale of numbers, expressive of the re¬
lative weights of the atoms of their elements :
Hydrogen . . . . . . 1
Oxygen . 7*5
Nitrogen . . . 5*0?
Carbon . 5*65
Sulphur . . . 15*0
Drs. Wollaston and Thomson, and Professor Berzelius, on
the other hand, have assumed oxygen as the decimal unit,
chiefly with a view to facilitate the estimation of its numerous
compounds with other bodies. This, perhaps, is to be regret¬
ted, even though the change may be in some respects eligible,
because it is extremely desirable that chemical writers should
employ an universal standard of comparison for the weights
of the atoms of bodies. It is easy, however, to reduce their
numbers to Mr. Dalton’s by the rule of proportion. Thus as
10 (the number of Drs. Wollaston and Thomson for oxygen)
is to 1*32 (their number of hydrogen) so very nearly is 7*5
(Mr. Dalton’s number for oxygen) to 1 (his number for hy¬
drogen).
Sir H. Davy has assumed, with Mr. Dalton, the atom of
hydrogen as unity ; but that philosopher, and Berzelius also,
have modified the theory, by taking for granted that water is
a compound of one proportion (atom) of oxygen, and two pro¬
portions (atoms) of hydrogen. This is founded on the fact,
that two measures of hydrogen gas and one of oxygen gas,
are necessary to form water; and on the supposition, that equal
measures of different gases contain equal numbers of atoms.
And as, in water, the hydrogen is to the oxygen by weight as
1 to 7*5, two atoms or volumes of hydrogen must, on this
hypothesis, weigh 1, and one atom or volume of oxygen 7*5,
or if we denote a single atom of hydrogen by 1, we must ex¬
press an atom of oxygen by 15. It is objectionable, however,
to this modification of the atomic theory, that it contradicts a
fundamental proposition of Mr. Dalton, the consistency of
which with mechanical principles he has fully shown ; namely,
vol. t. D
34
CHEMICAL AFFINITY, &C.
CHAP. II,
that when one combination only of two elements exists, as be¬
tween oxygen and hydrogen, it must be presumed, unless the
contrary can be proved, to be a binary one.
It is easy to determine, in the manner already explained, the
relative weights of the atoms of two elementary bodies, which
unite only in one proportion. But when one body unites, in
different proportions, with another, it is necessary, in order to
ascertain the weight of its atom, that we should know the
smallest proportion in which the former combines with the
latter. Thus, if we have a body A, 100 parts of which by
weight combine with not less than 30 of oxygen, the relative
weight of its atom will be to that of oxygen as 100 to 30 ; or,
reducing these numbers to their lowest terms, as 25 to 7*5 ;
and the number 25 will, therefore, express the relative weight
of the atom of A. But if, in the progress of science, it should
be found, that 100 parts of A are capable of uniting with 15
parts of oxygen, then the relative weight of the atom of A
must be doubled, for, as 100 to 15, so is 50 to 7*5. This
example will serve to explain the changes, that have been
sometimes made, in assigning the weights of the atoms of
certain bodies ; changes, which, it may be observed, always
consist either in a multiplication, or division, of the original
'weight, by some simple number.
There are (it must be acknowledged) a few cases, in which
one body combines with another in different proportions ; and
yet the greater proportions are not multiples of the less, by
any entire number. For example, we Iiave two oxides of iron,
the first of which consists of 100 iron and about 30 oxygen ;
the second of 100 iron and about 45 oxygen. But the num¬
bers 30 and 45 are to each other as 1 to 14. It will, however,
render these numbers (1 and 1-|) consistent with the law of
simple multiples, if we multiply each of them by 2, which
will change them to 2 and 3 ; and if we suppose that there is
an oxide of iron (though it has not yet been obtained experi¬
mentally), consisting of 100 iron and 15 oxygen; for the mul¬
tiplication of this last number by 2 and 3, will then give us
the known oxides of iron.
In some cases, where we have the apparent anomaly of 1
atom of one substance, united with of another, it has been
SECT. III.
CHEMICAL AFFINITY, &C.
35
proposed, by Dr, Thomson to remove the difficulty, by
multiplying both numbers by 2; and by assuming that, in
such compounds, we have 2 atoms of the one combined with
3 atoms of the other. Such combinations, it is true, are ex¬
ceptions to a law deduced by Berzelius ; that, in all inorganic
compounds , one of the constituents is in the state of a single
atom. But they are in no respect inconsistent with the views
of Mr. Dalton ; and are, indeed, expressly admitted by him
to be compatible with his hypothesis, as well as confirmed
by experience f. Thus it will appear, in the sequel, that
some of the compounds of nitrogen with oxygen are con¬
stituted in this way.
Several objections have been proposed to the theory of Mr.
Dalton ; but, of these, I shall notice only the most important.
1. It has been contended, that we have no evidence, when
one combination only of two elements exists, that it must be
a binary one ; and that we might equally well suppose it to be
a compound of two atoms of the one body, with one atom of
the other. In answer to this objection, we may urge the pro¬
bability that when two elementary bodies A and B unite, the
most energetic combination will be that in which one atom of
A is combined with one atom of B ; for an additional atom of
B will introduce a new force, diminishing the attraction of
those elements for each other, namely, the mutual repulsion
of the atoms of B ; and this repulsion will be the greater, in
proportion as we increase the number of the atoms of B.
2dly. It has been said, that, when more than one compound
of two elements exist, we have no proof which of them is the
binary compound, and which the ternary ; for example, that
we might suppose carbonic acid to be a compound of an atom
of charcoal and an atom of oxygen, and carbonic oxide to be
a compound of an atom of oxygen with two atoms of charcoal.
To this objection, however, it is a satisfactory answer, that
such a constitution of carbonic acid and carbonic oxide would
be directly contradictory of a law of chemical combination,
namely, that it is attended, in most cases, with an increase of
specific gravity. It would be absurd, therefore, to suppose
carbonic acid, which is the heavier body, to be only once com-
d 2
Thomson’s Annals, v. 187.
-f Thomson^ Annals, iii, 174.
36
CHEMICAL AFFINITY, &C.
CHAP. II,
pounded, and carbonic oxide, which is the lighter, to be twice
compounded. Moreover, it is universally observed, that of
chemical compounds, the most simple are the most difficult to
be decomposed ; and this being the case -with carbonic oxide, we
may naturally suppose it to be more simple than carbonic acid.
3dly. It has been remarked, that instead of supposing wa¬
ter to consist of an atom of oxygen united with an atom of
hydrogen, and that the atom of the former is 74- times heavier
than that of the latter, we might, with equal probability, con¬
clude that, in water, we have 74- times more atoms in number
of oxygen than of hydrogen. But this, if admitted, would
involve the absurdity, that in a mixture of hydrogen and
oxygen gases, so contrived that the ultimate atoms of each
should be in equal number, seven atoms of oxygen should
desert all the proximate atoms of hydrogen, in order to unite
with one at a distance, for which they must necessarily have a
less affinity. In this case, a less force must overcome a greater;
and, finally, only a small number of the atoms of hydrogen
would be engaged by the atoms of oxygen, the rest remaining
in a state of freedom.
It would be claiming too much, however, for the theory of
Mr. Dalton to assert that, in its present state, it is to be con¬
sidered as fully established in all its details. In the further
progress of chemical discovery, it is probable that it will re¬
ceive considerable modifications, and that the relative weights
of the atoms of bodies will, in many cases, be essentially
changed. The instances, in which the theory agrees with the
results of analysis, are already too numerous to allow them to
be considered as accidental coincidences ; and no phenomena
have hitherto been shown to be irreconcileable with the hypo¬
thesis. Its value and importance, if confirmed by the acces¬
sion of new facts, will be scarcely less felt as a guide to fur¬
ther investigations into the constitution of bodies, than as a
test of the accuracy of our present knowledge ; and the uni¬
versality of its application to chemical phenomena will be
scarcely inferior to that of the lawr of gravitation in explaining
the facts of natural philosophy*.
* A perspicuous and able statement of the atomic theory, published by
Mr. Ewart, in the sixth volume of Thomson's Annals, deserves the reader’s
perusal.
SECT. III.
CHEMICAL AFFINITY, & C.
37
A modification of the law of definite proportions, so far as
respects aeriform bodies, has been proposed by Gay Lussac,
namely, that they combine in proportions determinable not
by weight but by volume , the ratios being 1 measure of A to
1 of B, or 1 to 2, or 1 to 3, &c. Water, for example, re¬
sults from the union of 2 volumes of hydrogen with 1 volume
of oxygen ; muriate of ammonia from 1 volume of muriatic
acid gas + 1 of ammonia ; nitrous gas from 1 measure of
oxygen + 1 of nitrogen ; nitrous oxide from 1 oxygen + 2 ni¬
trogen ; nitrous acid from 2 oxygen + 1 nitrogen. In some
instances, as in that of water, this law is not inconsistent with
the atomic theory; but in other instances, it cannot be recon¬
ciled with the relative weights assigned to the atoms of certain
elementary bodies. In nitrous gas, for example, which Mr.
Dalton conceives to be formed by the union of 1 atom of
oxygen + 1 atom of nitrogen, equal volumes of those gases
would give for the relative weights of oxygen and nitrogen,
numbers differing widely from those derived by other methods.
The two hypotheses of atoms and of volumes cannot, therefore,
both be true ; and from some well ascertained exceptions to the
latter, it appears to me that the theory of volumes will scarcely
be found tenable.
Before dismissing the consideration of the proportions in
which bodies combine, it will be proper to notice a few gene¬
ral principles, which, though they are connected with the
atomic theory, have been derived from experience.
1. When we have ascertained the proportion in which any
two or more bodies ABC &c. of one class neutralize another
body X of a different class, it will be found that the same re¬
lative proportions of A B C See. will be required to neutralize
any other body of the same class as X. Thus, since 100 parts
of real sulphuric acid, and 68 (omitting fractions) of muriatic
acid neutralize 118 of potash, and since 100 of sulphuric acid
neutralize 71 of lime, we may infer that 68 of muriatic acid
will neutralize the same quantity (71) of lime. The great
importance of this law will readily be perceived, not only as it
enables us to anticipate, but also to correct, the results of
analysis.
2dly. If the quantities of two bodies, A and B, that are m>
38
CHEMICAL AFFINITY, &C.
CHAP. II.
cessary to saturate a given weight of a third body X, be re¬
presented by q and r, these quantities may be called equiva¬
lents. Thus, in the example above cited, 100 parts of sul¬
phuric acid and 68 of muriatic acid, are equivalents of each
other. A Table of Equivalents, which will be found extremely
useful in various calculations, will be given in the Appendix.
By adapting a table of this sort to a moveable scede, on the
principle of Gunter’s sliding rule, Dr. Wollaston has lately
constructed an instrument, called the Logornetric Scale of Che¬
mical Equivalents , which is capable of solving, with great
facility, a number of problems, interesting both to the scien¬
tific and practical chemist*.
SECTION IV.
Of Elective Affinity.
An important law of affinity, which is the basis of almost
all chemical theory, is, that one body has not the same force
of affinity towards a number of others, but attracts them un-
equally. Thus A will combine with B in preference to C,
even when these two bodies are presented to it under equally
favourable circumstances. Or, when A is united with C, the
application of B will detach A from C, and we shall have a
new compound consisting of A and B, C being set at liberty.
Such cases are examples of what is termed in chemistry simple
decomposition , by which it is to be understood that a body acts
upon a compound of two ingredients, and unites with one of
its constituents, leaving the other at liberty. And as the
forces of affinity of one body to a number of others vary, this
body has been metaphorically represented as making an elect¬
ion ; and the affinity has been called single elective affinity .
Thus if to the muriate of lime, consisting of lime and mu¬
riatic acid, we add potash, the muriatic acid exerts a stronger
* This instrument may be had, with printed instructions for its use, of
Mr. Carey, 182, Strand, London; and its cost is so trifling, that I consider
a plate of it to be quite unnecessary.
ECT. IV.
CHEMICAL AFFINITY, &C.
39
elective affinity for the potash than for the lime ; and the
lime falls down in the state of a powder, or is precipitated. Of
facts of this kind a great variety have been comprehended in
the form of tables, the first idea of which seems to have oc¬
curred nearly a century ago, to Geoffroy, a French chemist.
The substance, whose affinities are to be expressed, is placed
at the head of a column, and is separated from the rest by a
horizontal line. Beneath this line are arranged the bodies,
with which it is capable of combining, in the order of their
respective forces of affinity ; the substance which it attracts
most strongly being placed nearest to it, and that, for which
it has the least affinity, at the bottom of the column. The
affinities of muriatic acid, for example, are exhibited by the
following plan : —
MURIATIC ACID.
/
Barytes,
Potash,
Soda,
Lime,
Ammonia,
Magnesia,
&c. &c.
Simple decompositions may be expressed also by another
form, contrived by Bergman. Thus the following scheme il¬
lustrates the decomposition of muriate of magnesia by potash;-*
Muriate of Potash.
Muriate i Muriatic acid. Potash.
°*' . < Water at 60°.
Magnesia, i
& # Magnesia.
— """v — — '■ — ■ "
Magnesia.
The original compound (muriate of magnesia) is placed on
the outside and to the left of the vertical bracket. The in¬
cluded space contains the original principles of the compound,
and also the body which is added to produce decomposition.
Above and below the horizontal lines are placed the results of
their action. The point of the lower horizontal line being
40
CHEMICAL AFFINITY, &C.
CHAP. II.
turned downwards, denotes that the magnesia falls down or is
precipitated; and the upper line, being perfectly straight,
shows, that the muriate of potash remains in solution. If both
the bodies had remained in solution, they would both have
been placed above the upper line ; or, if both had been pre¬
cipitated, beneath the lower one. If either one or both had
escaped in a volatile form, this would have been expressed by
placing the volatilized substance above the diagram, and turn¬
ing upwards the middle of the upper horizontal line. But
since decompositions vary under different circumstances,
it is necessary to denote, by the proper addition to the
scheme, that the bodies are dissolved in water of the tem¬
perature of 60°.
No chemical facts can appear, on first view, more simple or
intelligible, than those which are explained by the operation
of single elective affinity. It will be found, however, on a
more minute examination, that this force, abstractedly con¬
sidered, is only one of several causes which are concerned in
chemical decompositions, and that its action is modified, and
sometimes even subverted, by counteracting forces.
SECTION V.
Of the Causes which modify the Action of Chemical Affinity.
The order of decomposition is not, as might be inferred
from the law of elective affinity, invariable ; but, in certain
cases, may even be reversed. Thus though A may attract B
more strongly than either A or B is attracted by C, yet, under
some circumstances, C may be employed to decompose par¬
tially the compound A B. Again, if we mix together A B and
C, using the two first in the proportions required to neutralize
each other, it will be found that A and B have not combined
to the exclusion of C, but that we have a compound of B with
A, and another of B with C, in proportions regulated by the
quantities of A and C, which have been employed. Facts of
this kind have been long known to chemists. It had been as¬
certained, for example, before the time of Bergman, that sub
SECT. V.
CHEMICAL AFFINITY, &C.
41
phate of potash, a salt composed of sulphuric acid and potash,
is partly decompounded by nitric acid, although the nitric has
a weaker affinity than the sulphuric acid for that alkali. Ex¬
amples of the same kind have since been multiplied by Ber-
thollet, who has asserted that in the following, as well as in
other cases, a substance possessing a weaker attraction, dis¬
places another having a stronger, for a third body # :
1. Potash separates sulphuric acid from barytes.
2. Lime separates sulphuric acid from potash.
3. Potash separates oxalic acid from lime.
4. Nitric acid separates lime from oxalic acid.
5. Potash separates phosphoric acid from lime.
6. Potash separates carbonic acid from lime.
7. Soda separates sulphuric acid from potash.
These facts, and a variety of similar ones, are to be explained,
according to the viewrs of Berth oil et, on the following prin¬
ciples : —
1. When two substances are opposed to each other with re¬
spect to a third, as in the foregoing examples, they may be
considered as antagonist forces ; and they share the third body
between them in proportion to the intensity of their action*
But this intensity, according to Berth ol let, depends not only
on the energy of the affinities , but on the quantities of the two
bodies opposed to each other. Hence a larger quantity of
one of the substances may compensate a weaker affinity, and
the reverse. To the absolute weight of a body, multiplied by
the degree of its affinity, he has given the name of mass, a
term in some degree objectionable from the different mean¬
ing which is affixed to it in mechanical philosophy. As an
illustration, let us suppose (what is not accurate in point of
fact) that the affinity of barytes for muriatic acid is twice as
strong as that of potash, or that these affinities are respectively
denoted by the numbers 4 and 2. In this case the same mass
will result from 4 parts of barytes as from 8 of potash ; be-
* In each of the examples given in the Table, the body, first mentioned,
decomposes a compound of the second and third, although its attraction for
the second is inferior to that of the third.
42
CHEMICAL AFFINITY, &C.
CHAP. II.
cause the same product (16) is obtained in each instance, by
multiplying the number indicating the affinity into that de¬
noting the quantity ; for 4 (the affinity of barytes) multiplied
by 4, (the quantity assumed in this example) is equal to 16 ;
and 2 (the affinity of potash) multiplied by 8 (its quantity) is
also equal to 16. In this case, therefore, to divide equally a
portion of muriatic acid between barytes and potash, these
bodies should be employed in the proportion of 2 of the former
to 4 of the latter.
The influence of quantity explains also the difficulty which
is observed in effecting, in any instance, the total decomposi¬
tion of a compound of two principles by means of a third. The
immediate effect of a third body C, when added to a compound
A Ij, is to abstract from B a portion of the substance A ;
and consequently a portion of B is set at liberty, the attrac¬
tion of which for A is opposed to that of the uncombined
part of C. The farther this decomposition is carried, the
greater will be the proportion of B, which is brought into an
uncombined state ; and the more powerfully will it oppose any
farther tendency of C to detach the substance A. At a cer¬
tain point, the affinities of B and C for A will be exactly ba¬
lanced, and the decomposition will proceed no farther. In a
few cases, it is acknowledged by Berthollet, a third body se¬
parates the whole of one of the principles of a compound ;
but this he supposes to happen in consequence of the agency
of other extraneous forces, the nature of which remains to be
pointed out.
2dlv. Cohesion is a force, the influence of which over the
chemical union of bodies has already been explained in a
former section ; and other illustrations of its interference will
be given, when we consider the subject of the limitations to
chemical combination.
Sdly. Insolubility is another force, which essentially modifies
the exertion of affinity. It is to be considered, indeed, merely
as the result of cohesion, with respect to the liquid in which
the effect takes place.
When a soluble substance and an insoluble one are pre¬
sented, at the same time, to a third, for which they have
nearly an equal affinity, the soluble body is brought into the
SECT, V.
CHEMICAL AFFINITY, &C.
43
sphere of action with great advantages over its antagonist. Its
cohesion at the outset is but little, and by solution is reduced
almost to nothing ; while that of the insoluble body remains
the same. The whole of the soluble substance also exerts its
affinity at once; while a part only of the insoluble one can
oppose its force. Hence the soluble substance may prevail,
and may attach to itself the greatest proportion of the third
body, even though it has a weaker affinity than the insoluble
one to the subject of combination.
Insolubility, however, under certain circumstances, is a
force which turns the balance in favour of the affinity of one
body when opposed to the affinity of another. For example,
if to the soluble compound, sulphate of soda, we add barytes,
the new compound, sulphate of barytes, is precipitated the
instant it is formed: and being removed from the sphere of
action, the soda can exert no effect upon it by its greater
quantity or mass. For the same reason, when soda is added
to sulphate of barytes, the sulphate is protected from decom¬
position both by its insolubility and by its cohesion.
These facts sufficiently prove that the order of precipitation,
which was formerly assumed as the basis of tables of elective
affinity, can no longer be considered as an accurate measure
of that force ; and that the body, which is precipitated, may,
in some cases, be superior in affinity to the one which has
caused precipitation. In these cases, a trifling superiority in
affinity may be more than counterbalanced by the cohesive
force, which causes insolubility.
4thly, Great specific gravity is a force, which must concur
with insolubility or cohesion in originally impeding combina¬
tion; and when chemical union has taken place, it must come
in aid of affinity, by removing the new compound from the
sphere of action. It is scarcely necessary to enlarge on the
operation of a force, the nature of which must be so obvious.
5thly. Elasticity. Cohesion, it has already been stated,
may prove an impediment to combination ; and on the other
hand, it is possible that the particles of bodies may be sepa¬
rated so widely, as to be removed out of the sphere of their
mutual attraction. Such appears to be the fact with regard
to a class of bodies called airs or gases. The bases of several
3
44
CHEMICAL AFFINITY, &C,
CHAP. IT.
of these have powerful attractions for the bases of others, and
for various liquids, and yet they do not combine on simple
admixture, but strong mechanical pressure brings their par¬
ticles sufficiently near, to be within the influence of their
mutual attraction, and combination immediately ensues.
Again if two bodies, one of which has an elastic and the
other a liquid form, be presented at the same time to a solid,
for which they have both an affinity, the solid will unite with
the liquid in preference to the gas. Or if we add to the com¬
pound of an elastic substance with an inelastic one, a third
body also inelastic, the two latter combine to the exclusion of
the elastic body. For example, if to the compound of pot¬
ash and carbonic acid we add sulphuric acid, the latter acid,
acting both by its affinity and its quantity, disengages a por¬
tion of carbonic acid. This, by its elasticity, is removed from
the sphere of action, and presents no obstacle to the farther
operation of the sulphuric acid. Hence elastic bodies act
only by their affinity ; whereas liquids act both by their affi¬
nity and quantity conjoined. And though the affinity of the
liquid, abstractedly considered, may be inferior to the affinity
of the elastic body, yet, united with quantity, it prevails. In
the above instances, the whole of the elastic acid may be ex¬
pelled by the fixed acid ; whereas, as it has already been ob¬
served, decomposition is incomplete, if the substance which
is liberated remain within the sphere of action.
6thly, Efflorescence is a circumstance which occasionally in¬
fluences the exertion of affinity; but this is only of very rare
occurrence. . The simplest example of it is that of lime, and
muriate of soda. When a paste composed of these two sub¬
stances with a great excess of lime, is exposed, in a moist
state, to the air, the lime, acting by its quantity, disengages
soda from the common salt, which appears in a dry form, on
the outer surface of the paste, united with carbonic acid ab¬
sorbed from the atmosphere. In this case the soda, which is
separated, being removed from contiguity with the interior part
of the mass, presents no obstacle to the farther action of the
lime, and the decomposition is carried farther than it would
have been, had no such removal happened.
7thly. The influence of temperature over chemical affinity
SECT. V.
CHEMICAL AFFINITY, &C.
45
is extremely extensive and important ; but at present a very
general statement only of its effects is required. In some
cases an increased temperature acts in promoting, and at
others in impeding, chemical combination : and it materially
affects also the order of decompositions.
An increased temperature promotes chemical union by
diminishing or overcoming cohesion. Thus metals unite by
fusion, and several salts are more soluble in hot that in cold
water. Whenever heat is an obstacle to combination, it pro¬
duces its effect by increasing elasticity. Hence water absorbs
a less proportion of gas at a high than at a low temperature.
A reduction of the temperature of elastic bodies, by lessening
their elasticity, facilitates their union with other substances.
In certain cases, an increased temperature has the combined
effects of diminishing cohesion and increasing elasticity.
When sulphur is exposed to oxygen gas, no combination
ensues, until the sulphur is heated ; and though the elasticity
of the gas is thus increased, yet the diminution of cohesion
of the solid is more than proportionate, and chemical union
ensues between the two bodies.
8thly. The electrical state of bodies has a most important
influence over their chemical union. This, however, is a
subject, of which it would be difficult to offer a general view",
and for its full development, I refer to a subsequent chapter
on Electro-chemistry .
9thly. Mechanical pressure is another force, which has con¬
siderable influence over chemical affinity. WTith respect to
solid bodies, its agency is not frequent ; but we have unequi¬
vocal examples of its operation in cases, where detonation is
produced by concussion. The effects of pressure are chiefly
manifested, in producing the combination of aeriform bodies
either with solids, with liquids, or with each other ; and in
preserving combinations, which have been already formed,
under circumstances tending to disunite them. Chalk, for
example, is a compound of lime and carbonic acid ; and
these bodies, by the simple application of an intense heat,
are separable from each other ; but, under strong pressure, a
heat may be applied sufficient to melt the chalk, without ex¬
pelling the carbonic acid. It is this principle, (of the in-
46
CHEMICAL AFFINITY, &C.
CHAP. II.
fiuence of pressure in opposing chemical decomposition,) that
is the foundation of Dr. Hutton’s ingenious Theory of the
Earth.
Such are the most important circumstances, that modify
the exertion of cheminal affinity. Of their influence, suf¬
ficient illustrations have been given to prove, that in every
case of combination and decomposition, we are not to con¬
sider the force of affinity abstractedly ; but are to take into
account the agency of other powers, as cohesion, quantity,
insolubility, elasticity, efflorescence, and temperature. By the
action of these extraneous powers, Berthollet has endeavoured
to explain certain facts which are not easily understood on
any other principle. Of these the most important are, lstly,
the establishment of proportions in chemical compounds;
and 2dly, the modification produced in the affinities of bodies
by chemical union.
1. Independently of these extraneous forces, Berthollet
imagines that there are no limits to combination, or that two
bodies, which are now susceptiple of union only in one or in
few' proportions, might, if these forces were annihilated, be
united in every proportion. The causes which he has as¬
signed, as chiefly regulating proportion, are cohesion and
elasticity. To take one of the simplest cases, the proportion,
in which a salt can be combined with water, depends on the
balance between the chemical affinity of the bodies for each
other, and the cohesive attraction of the salt. In this case,
then, cohesion is the limiting power. As an example of the
influence of this force when more energetic affinities are ex¬
erted, if wre add to diluted sulphuric acid a solution of barytes,
a compound is formed, consisting of sulphuric acid and
barytes, which, in consequence of its great insolubility or co¬
hesion, is instantly removed from contact with the redundant
acid, and with established proportions.
The agency of elasticity in limiting proportion, may be
exemplified by the combination of hydrogen and oxygen. If
a mixture of the two gases be inflamed, the new compound,
water, is immediately separated, from what is superfluous ol
both ingredients, by its superior density. In other instances,
the bases of aeriform substances are combined in various
SECT. V.
CHEMICAL AFFINITY, &C.
47
proportions, and in such examples, there are several terms
of greatest condensation, as in the case of oxygen and ni¬
trogen.
2. Another important part of the theory of Rerthollet is,
that the affinities of a compound are not newly acquired ; but
are merely the modified affinities ol its constituents, the action
of which, in their separate state, was counteracted by the
prevalence of opposing forces. By combination, these forces
are so far overcome, that the affinities of the constituents are
enabled to exert themselves.
The action of different affinities existing in one compound,
Berthollet terms resulting affinities , while the individual affi¬
nities of the constituents he calls elementary affinities. Thus
nitric acid acts on potash by an affinity, which results from those
of oxygen and azote for potash. And as ail affinity is mutual,
the term resulting affinity is applied, also, to that force, with
which a simple body acts on a compound ; to the affinity for
example, which any simple body may exert on nitric acid.
A simple body, indeed, may exert towards a compound both
an elementary and resulting affinity. If the elementary affi¬
nity prevails, it will unite only with one of the principles of
the compound, as when a simple body, by its affinity for
oxygen, decomposes nitric acid, and liberates its nitrogen in
a separate form. If the resulting affinity be predominant,
the simple body will unite with the whole compound without
effecting any disunion of its elements.
From these views it may be inferred, that wre are not, in any
case, to deny the existence of an affinity between two bodies,
merely because they do not combine when presented to each
other ; for an affinity may exist, but may be suppressed by
the prevalence of opposing forces. According to the doctrine
of Berthollet, affinity is a force exerted by every body towards
every other; even though not made apparent by any effect.
On this principle, we are able to explain certain phenomena,
which are wholly unintelligible on any other, and especially
those which have been referred to disposing affinity . The
action of sulphuret of potash, for example, on oxygen gas,
has been ascribed to the disposing affinity of potash for sul¬
phuric acid. This, however, is ascribing an affinity to a
48
CHEMICAL AFFINITY, &C.
CHAP. II.
compound, before that compound has existence. It is much
more probable, that besides the diminished cohesion of the
sulphur, the affinity of potash for oxygen has some share in
producing the combination. On this principle the united
affinities of the potash and sulphur for oxygen (in other
words the resulting affinities of the sulphuret of potash) are
the efficient causes of chemical union. This explanation, at
least, does not, like the theory of disposing affinities, involve
an absurdity.
The theory of Berthollet, however, which promised, on
its first development, to form a new era in chemical philosophy,
has lost much of its probability, by the subsequent progress
of the science. It is directly, indeed, at variance with the
doctrine of definite proportions, which every day gathers
strength by the accumulation of new and well established facts.
It is liable, moreover, to the following objections.
1st. It has been shown by Professor PfafF, of Kiell *, that,
in various cases, where two acids are brought into contact
with one base, the base unites with one acid, to the entire
exclusion of the other. When, for example, to a given
weight of lime, quantities of sulphuric and tartaric acids are
put, either of which would exactly saturate the lime, the sul¬
phuric acid unites with the lime, to the entire exclusion of the
tartaric. The same evidence of a superior affinity of the
sulphuric acid over that of the oxalic is obtained, by placing
those acids in contact with as much oxide of lead, as would
exactly saturate either of them. Again, comparing the action
of two bases on one acid, the same law is found to hold good:
for when potash and magnesia are mixed with just as much
sulphuric acid, as is required to saturate either of them, the
potash seizes the whole of the acid, and no part of it unites
with the magnesia. Nor can these effects be explained by any
of those extraneous forces, which Berthollet supposes, in all
cases, to regulate chemical combination ; or by any principle,
but a stronger affinity of sulphuric acid, than of tartaric or
oxalic acid, for the different bases; and of potash, than of
magnesia, for the same acid.
*
77 Ann. de Chim. p. 259.
SECT. V.
CHEMICAL AFFINITY, &C,
2dly. Some of the eases, before quoted from Berthollet, to
show the reciprocal displacement of two bodies by each other
from a third (it has been justly observed), are examples, not
of single elective affinity, in which three bodies only are con¬
cerned; but of complex affinity, in which the attractions of
four bodies are brought into action. In the first case, for
example, there is reason to believe, that sulphuric acid is dis-
placed from barytes, not by pure potash, but by potash which
has absorbed carbonic acid from the atmosphere.
3dly. In other cases, the consideration of the affinities of
two bodies A and B, for a third C, is complicated with thi*
circumstance, that the neutral compound of A and B has an
affinity for a farther portion of one of its ingredients. If then
C be brought into contact with the compound A B, we have,
acting at the same moment, the affinity of C for A, which
partly decomposes the compound A B ; and the affinity of the
undecomposed part of A B, for that portion of B which is set
at liberty. For instance, when nitric acid acts on sulphate of
potash, some nitrate of potash is formed ; and the sulphuric
acid, which is set at liberty, uniting with the undecomposed
sulphate of potash, composes a new salt, consisting of sulphate
of potash with an excess of sulphuric acid.
4thly. It is a strong objection to the theory of Berthollet
that, in some cases, decompositions happen, which, according
to his views, ought not to take place; and that in others, de¬
compositions do not ensue, which the theory would have led
us to have anticipated.
5thly. The theory is objectionable, inasmuch as, in several
instances, properties are supposed to operate, before the bodies
exist, to which those properties are attributed. It is incon¬
ceivable, for instance, that the cohesion, or insolubility, of
sulphate of barytes, can have any share in producing the de¬
composition of sulphate of potash by that earth ; for the inso¬
lubility of sulphate of barytes can have no agency, till that
compound is formed; which is the very effect to be explained.
Notwithstanding these objections to the theory of Berthol¬
let, when carried so far as has been done by its author, in the
explanation of chemical phenomena, it must still be admitted
that the extraneous forces, pointed out by that acute phiioso-
VOL. I. E
5a
CHEMICAL AFFINITY, &C.
CHAP. II.
pher, have great influence in modifying the effects of chemical
affinity. But these forces are entitled only to be considered
as secondary causes ; and not as determining combinations or
decompositions, nor as regulating the proportions in which
bodies unite, independently of the superior force of chemical
affinity.
SECTION VL
Of the Estimation of the Forces of Affinity .
The affinities of one body for a number of others are not
all of the same degree of force. This is all that the present
state of our knowledge authorizes us to affirm; for we are
ignorant how much the affinity of one body for another is
superior to that of a third. The determination of the precise
forces of affinity would be an important step in chemical phi¬
losophy : for its phenomena would then be reduced to calcu¬
lation ; and we should be enabled to anticipate the results of
experiment. That the force of chemical affinity must be pro¬
digiously great, is evident from its effect in preserving the com¬
bination of water with some bodies (the alkalies for instance)
when exposed to a violent heat ; notwithstanding its great ex¬
pansive force, and though water is not essential to the consti¬
tution of those bodies.
The observed order of decomposition, it has already been
stated, does not enable us to assign the order of the forces of
affinity ; because, in all decompositions, other forces are con¬
cerned. We are, therefore, obliged to seek some other method
of determining the problem. Of these several have been pro¬
posed.
When the surface of one body is brought into contact with
another surface of the same kind, as when the smooth surfaces
of a divided leaden bullet are pressed together, they adhere
by the force of cohesion, their particles being all of the same
kind . But when the surfaces of different bodies are thus
brought into apparent contact, it is reasonable to suppose-
that their adhesion arises from chemical affinity, because their
particles are of different kinds, Guyton proposed, therefore*
SECT. VI.
CHEMICAL AFFINITY, &C.
51
the comparative force, with which different surfaces adhere,
as a competent measure of chemical affinity. His experiments
were made on plates of different metals, of precisely the same
size and form, suspended by their centres from the arm of a
sensible balance. The lower surfaces of these plates were
successively brought into contact with mercury, which was
changed for each experiment, and the weight was observed,
which it was necessary to add to the opposite scale, in order
to detach the several metals. Those which required the largest
weight were inferred to have the greatest affinity; and it is
remarkable, that the order of affinities, as determined in this
way, correspond with the affinities as ascertained by other
methods. The following were the results :
Gold adhered to mercury with a force of . . . . 446 grains.
Silver . . . . . 429
Tin . . . . . . . . . 418
Lead . 397
Bismuth . . . 372
Zinc . 204
Copper . ...» . 142
Antimony . 126
Iron . 115
Cobalt . 8
This method, it must be obvious, is of too limited applica¬
tion to be of much utility ; for few bodies have the mechanical
conditions, which can enable us to subject them to such a test.
How, for example, could the affinities of acids for alkalies be
examined on this principle? It may be doubted, also, whe¬
ther in the cases to which it may be applied, it does not mea¬
sure the facility of combination, rather than the actual force
of affinity.
To determine the absolute forces of affinity, which one body
exerts towards a number of others, Mr. Kirwan has proposed
the quantity of each which is required to produce neutrali¬
zation, in other words, its equivalent. This he has ascertained
by experiment in a great variety of instances, a few of which
are contained in the following tables; the numbers being
altered, to accommodate them to recent discoveries.
E 2
52
CHEMICAL AFFINITY, &C.
CHAP. II.
100 Parts of
SULPHURIC ACID
require for Neutralization
r~~~ — “ — - * - — ■ — - >
194- parts of barytes.
138 .... of strontites.
118 .... of potash.
78*2 .... of soda.
71 .... of lime.
49*2 .... of magnesia.
43 .... of ammonia.
100 Parts of
potash require
115 of nitric acid.
93 of carbonic acid.
84*5 of sulphuric.
58 of muriatic.
In judging of the affinities of the same acid for different
bases, Mr. Kirwan assumed that they are represented by the
numbers indicating the quantities of each base required for
neutralization. Thus, because 100 parts of sulphuric acid
neutralize 194 of barytes, and 118 of potash, the affinity of
the former is superior to that of the latter in the proportion of
194 to 118. So far the inference corresponds with the order
of decomposition; for barytes takes sulphuric acid from
potash. But if we examine the affinities of potash, as re¬
presented in the second table, we shall find that, on this
principle, they are directly contradictory to fact. Thus the
affinity of sulphuric acid should be inferior to that of the car¬
bonic ; whereas it is well known that the former displaces the
latter from all its combinations. Mr. Kirwan was, therefore,
driven to the necessity of establishing a precisely opposite rule
in determining the affinities of different acids for the same base,
and of assuming that they are inversely proportionate to the
affinity of the saturating acid. Thus the affinity of carbonic
acid for potash would be represented by 84*5, and that of sul¬
phuric acid 93. This, however, involves a contradiction;
since it is implied that a stronger affinity, in one instance, re¬
quires a greater quantity of the saturating principle, as in the
relation of barytes and potash to sulphuric acid ; and that, in
the other, it requires a less quantity, as in the instance of the
sulphuric and carbonic acids with respect to potash.
Since neutralization is an effect of chemical affinity, which
must in all cases bear a proportion to its cause, it has been
assumed by Berthollet, that the substance which, in the
1
SECT. VII. CHEMICAL AFFINITY, &C. 5$
smallest quantity , neutralizes another, is the one possessing
the strongest affinity. On this principle the affinities of sul¬
phuric acid for different bases, will be exactly the reverse of
the order established by Mr. Kirwan; and to that order,
which would have been assigned from observed decomposi¬
tions. Thus ammonia will have a stronger affinity for sul¬
phuric acid, than any of the substances which are placed above
in the table ; though it is separated, by each of these, from
its union with that acid.
It is in the extraneous forces, which have been enumerated
as influencing chemical affinity, that we are to seek, according
to Berthollet, for the explanation of this apparent anomaly,
and especially in the forces of cohesion and elasticity® The
elasticity of ammonia, for example, turns the balance in favour
of magnesia, lime, &c. There is an obvious difficulty, how¬
ever, in the application of the theory. For as the elasticity
of ammonia is suppressed by its combination with sulphuric
acid, what, it may be asked, but a superior affinity for sul¬
phuric acid, existing in the substances which stand above am¬
monia in the table, can occasion the first commencement of
decomposition ? The problem, therefore, of determining the
absolute forces of affinity can scarcely be admitted to be solved.
Even if it were, we should not be able to predict the order of
decomposition, unless the modifying forces of cohesion, elas¬
ticity, &c. could be at the same time subjected to precise ad¬
measurement. Until both these objects are accomplished, the
results of chemistry can in no case be obtained by calculation,
but the science must remain a collection of general principles^
derived from experiment and induction.
SECTION VIL
Of Complex Affinity .
Under the more general name of complex affinity , Berthol¬
let includes that which has hitherto been considered as pro¬
duced by the action of four affinities, and which has com¬
monly been denominated double elective affinity. It frequently
happens that the compound of two principles cannot be de-
CHEMICAL AFFINITY, &C.
CHAP. II,
54?
stroyed either by a third or a fourth separately applied ; but
if the third and fourth* be combined, and placed in contact
with the former compound, a decomposition, or a change of
principles will ensue. Thus when lime water is added to a
solution of the sulphate of soda, no decomposition happens,
because the sulphuric acid attracts soda more strongly than it
attracts lime. If the muriatic acid be applied to the same
compound, still its principles remain undisturbed, because the
sulphuric acid attracts soda more strongly than the muriatic.
But if the lime and muriatic acid, previously combined, be
mixed with the sulphate of soda, a double decomposition is
effected. The lime, quitting the muriatic acid, unites with
the sulphuric ; and the soda, being separated from the sul¬
phuric acid, combines with the muriatic. These decompo¬
sitions are rendered more intelligible by the following diagram,
contrived by Bergman.
Muriate of Soda
Sulphate
of
Soda
V
Soda
78 }>
115
Muriatic acid
< 10'1 >
Su!phc acid 71
Lime
Sulphate of Lime
Muriate
of
Lime
On the outside of the vertical brackets are placed the ori¬
ginal compounds ; and above and below the diagram, the new
compounds. The upper line, being straight, indicates that
the muriate of soda remains in solution ; and the middle of
the lower line, being directed downwards, that the sulphate
of lime is precipitated.
In all cases similar to the foregoing, Mr. Kirwan Conceives
that we may trace the operation of two distinct series of affini¬
ties. i he affinities tending to preserve the original compounds
(which in the above example are those between sulphuric acid
and soda, and between muriatic acid and lime), he terms the
quiescent affinities; because they resist any change of composi¬
tion. On the other hand the affinities, which tend to disunite
SECT. VII. CHEMICAL AFFINITY, &C. 5B
the original compounds and to produce new ones (such as
those between muriatic acid and soda, and between sulphuric
acid and lime), he terms divellent affinities. In order that an
effect may be produced, the divellent affinities must necessarily
be superior to the quiescent. Now, assuming the numbers in
Mr. Kirwan’s tables to express accurately the forces of affini¬
ties, the double exchange of principles, which happens in the
preceding instance, is readily explained. Thus the quiescent
affinities are
Those of lime to muriatic acid = 104
of soda to sulphuric acid = 78
182
The divellent affinities, opposed to these, consist of
The affinity of soda to muriatic acid = 115
lime to sulphuric acid = 71
186
The original compound, therefore, is preserved by a force
equivalent to 182, and the tendencies to produce new com*
pounds are represented by the number 186. The divellent
affinities are, therefore, predominant.
The theory of quiescent and divellent affinities, however,
though highly attractive from its simplicity, and from the
facility with which it solves certain phenomena, is completely
defective in the explanation of others. For example, sulphate
of potash is decomposed by muriate of barytes. Yet, esti¬
mating in the above manner the quiescent and divellent affi¬
nities, an exchange of principles ought not to ensue. The
affinities tending to preserve the original compound, are those
of sulphuric acid for potash = 118, and of muriatic acid for
barytes = 285. The divellent affinities are that of muriatic
acid for potash = 174 + that of sulphuric acid for barytes
= 194. The quiescent affinities then are 118 + 285 = 403,
and the divellent 174 + 194 =.368. This leaves a balance of
35 in favour of the quiescent affinities ; and yet decomposition
ensues, when the two compounds are brought into contact.
56
CHEMICAL AFFINITY, &C.
CHAP. II.
It must be acknowledged that the numbers, assumed by Mr.
Kirwan, do not correspond with the actual forces of affinity.
But even if they are taken according to the principle assumed
by Berthollet, they will not be found universally applicable.
The reason of this is, that the phenomena produced by com¬
plex affinity, like those occasioned by simple affinity, are ma¬
terially influenced by the extraneous forces of cohesion, quan¬
tity, elasticity, temperature, &c. The effect of quantity is
shown by the fact, that if two salts be mixed together in cer¬
tain proportions, decomposition will ensue, but not if mixed
in other proportions. Thus from the mingled solutions of
two parts of muriate of lime and one of nitrate of potash, wre
obtain muriate of potash ; but not from equal weights of the
two salts. Insolubility, or precipitation, has also a consider¬
able influence on the result. When this occurs, the influence
of quantity is destroyed, as in the case of sulphate of potash
and muriate of barytes. Elasticity, and an increased tempe¬
rature (which operates by increasing elasticity), and the re¬
verse of this, or a greatly diminished temperature, have also a
powerful influence in promoting the action of complex affi¬
nities. Thus of four principles, two of which are volatile
and two fixed, the two which are volatile will be disposed
to unite, in preference to combining with either of those
which are fixed. The nature of the fluid, in which salts
are dissolved, has also an important influence on their ten¬
dency to mutual decomposition*. Thus changes take place
In the midst of an alcoholic medium, which do not hap¬
pen to the same bodies dissolved in water t. We have even
Instances, in which though a compound A B decomposes an¬
other compound C D, A uniting with C, and B with D, yet
(which could not have been expected a priori ) the compound
A C is reciprocally decomposed by D B, and the original
compounds A B and C D are regenerated if. Hence the phe¬
nomena of complex decomposition concur with those of a
more simple kind, in proving that affinity is not an uniform
force, but is materially influenced by various modifying cir-
* Ann. de Chim. et Phys. iv. 366. f Dr. Murray on Sea Water:
| See the sect, on Sulphate of Barytes.
SECT. VII.
CHEMICAL AFFINITY, &C.
57
cumstances ; and that we cannot confidently anticipate results,
from comparing the numerical expressions of quiescent and
divellent affinities.
One great obstacle to the construction of tables, capable of
representing the forces of affinity, is the difficulty of ascer¬
taining, with precision, the quantities of bodies required for
neutralization. Notwithstanding all the care employed by Mr.
Kirwan, considerable errors appear to have crept into the
results of his experiments. This will sufficiently appear, when
they are examined by a test, originally proposed by Guyton.
It must be obvious that if between two salts, which are mixed
together in solution, decomposition should ensue, and the
mixture should afterwards be found neutral, the quantity of
acid, which has quitted one of the bases, must have been
exactly equivalent to the saturation of the other base, also
deserted by its acid. If, for example, we mingle the muriate
of magnesia and sulphate of soda, the mixture continues neu¬
tral ; and hence it follows that the muriatic acid, which has
quitted the magnesia, must have been exactly equal to the
neutralization of the soda, deserted by the sulphuric acid.
But from a calculation, founded on the proportion of the in¬
gredients of these salts, as established by Mr. Kirwan, it ap¬
pears that the soda, detached from the sulphuric acid, is not
adequate to the saturation of the muriatic acid. The mix—
tuie, iheiefoie, ought to be acid ; and since this is contrary
to fact, we may safely infer that there is an error in the esti¬
mation of the ingredients composing these salts. No tables,
indeed, can be correct, unless they stand the test of this mode
of verification. Such a table has been calculated by Fischer
from the experiments of Richter; but even this table seems
in several respects to be of questionable accuracy. I have
thought it, however, entitled to a place among the tables in
the Appendix ; and I shall annex, also, a more correct one,
the data of which are chiefly supplied by Dr. Wollaston’s
paper on Chemical Equivalents*.
* Phil. Trans. 1814,
58
CHEMICAL AFFINITY, &C.
CHAP. II
SECTION VIII.
Experimental Illustrations of Chemical Affinity, Solution , &c.
For these experiments, a few wine glasses, or, in preference,
deep ale glasses, will be required; and a Florence flask for
performing the solutions.
I. Some bodies have no affinity for each other . — Oil and
water, mercury and water, or powdered chalk and water, when
shaken together in a vial, do not combine, the oil or water
always rising to the surface, and the mercury or chalk sinking
to the bottom.
II. Examples of chemical affinity , and its most simple effect ,
viz . solution.— Sugar or common salt disappears or dissolves
in water; chalk in dilute muriatic acid*. Sugar and salt are,
therefore, said to be soluble in water, and chalk in muriatic
acid. The liquid in which the solid disappears is termed a
solvent or menstruum. Chalk or sand, on the contrary, when
mixed with water by agitation, always subsides again. Hence
they are said to be insoluble.
III. Influence of mechanical division in promoting the action
of chemical affinity , or in favouring solution. — Lumps of chalk
or marble dissolve much more slowly in dilute muriatic acid,
than equal weights of the same bodies in powder. Muriate
of lime, or nitrate of ammonia, cast, after liquefaction by heat,
into the shape of a solid sphere, is very slowly dissolved ; but
with great rapidity when in the state of a powder or of crystals.
When a lump of the Derbyshire fluate of lime is immersed in
concentrated sulphuric acid, scarcely any action of the two
substances on each other takes place ; but if the stone be finely
pulverized, and then mingled with the acid, a violent action is
manifested, by the copious escape of vapours of fluoric acid.
In the common arts of life, the rasping and grinding of wood
and other substances are familiar examples.
IV. Hot liquids , generally speaking , are more powerful sol¬
vents than cold ones.— To four ounce-measures of water, at the
temperature of the atmosphere, add three ounces of sulphate
* I omit, purposely, the distinction between the solution and dissolution.
SECT. VIII.
CHEMICAL AFFINITY, &C.
59
of soda in powder. Only part of the salt will be dissolved,
even after being agitated some time. Apply heat, and the
whole of the salt will disappear. When the liquor cools, a
portion of salt will separate again in a regular form or in crys¬
tals. This last appearance affords an instance of crystallization.
To this law, however, there are several exceptions ; for
many salts, among which is muriate of soda, or common salt,
are equally, or nearly equally, soluble in cold as in hot water.
(See the table of solubility of salts in water, in the Appendix.)
Hence, a hot, and saturated solution of muriate of soda does
not, like the sulphate, deposit crystals on cooling. To obtain
crystals of the muriate, and of other salts which observe a si¬
milar law as to solubility, it is necessary to evaporate a por¬
tion of the water ; and the salt will then be deposited, even
while the liquor remains hot. In general, the more slow the
cooling, or evaporation, of saline solutions, the larger and
more regular are the crystals.
V. A very minute division of bodies is effected by solution.—
Dissolve two grains of sulphate of iron in a quart of water,
and add a few drops of this solution to a wine-glassful of water,
into which a few drops of tincture of galls have been fallen.
The dilute infusion of galls will speedily assume a purplish
hue. This shows that every drop of the quart of water, in
which the sulphate of iron was dissolved, contains a notable
portion of the salt.
VI. Some bodies dissolve much more readily and copiously than
others. — Thus, an ounce measure of distilled water will dissolve
half its weight of sulphate of ammonia, one third its weight of
sulphate of soda, one sixteenth of sulphate of potash, and only
one five-hundredth its weight of sulphate of lime.
VII. Mechanical agitation facilitates solution. — -Into a wine-
glassful of water, tinged blue with the infusion of litmus, let
fall a small lump of solid tartaric acid. The acid, if left at rest,
even during some hours, will only change to red that portion
of the infusion which is in immediate contact with it. Stir the
liquor, and the whole will immediately become red.
VIII. Bodies do not act on each other , unless either one or both
‘ be in a state of solution , or at least contain water. — 1. Mix some
dry tartaric acid with dry bi-carbonate of soda, and grind
2
60
CHEMICAL AFFINITY, &C.
CHAP. II.
them together in a mortar. No combination will ensue till
water is added, which, acting the part of a solvent, promotes
the union of the acid and alkali, as appears from a violent
effervescence. It has been shown by Link*, that the water of
crystallization, existing in certain salts, acts as free water in
occasioning chemical action. For example, acetate of lead
and sulphate of copper, both in crystals, become green when
triturated together, a proof of the mutual decomposition of
those two salts.
2. Spread thinly, on a piece of tinfoil, three or four inches
square, some dry nitrate of copper f, and wrap it up. No ef¬
fect will follow. Unfold the tinfoil, and having sprinkled the
nitrate of copper with the smallest possible quantity of water,
wrap the tinfoil up again as quickly as possible, pressing down
the edges closely. Considerable heat, attended with fumes,
will now be excited ; and, if the experiment has been dex¬
terously managed, even light will be evolved. This shows
that nitrate of copper has no action on tin, unless in a state
of solution.
IX. Bodies , even when in a state of solution, do not act on each
other at perceptible distances ; in other words, contiguity is es¬
sential to the action of chemical affinity. — Thus, when two
fluids of different specific gravities, and which have a strong
affinity for each other, are separated by a thin stratum of a
third, which exerts no remarkable action on either, no combi¬
nation ensues between the uppermost and lowest stratum.
Into a glass jar, or deep ale glass, pour two ounce-measures
of a solution of subcarbonate of potash, containing, in that
quantity, two drachms of common salt of tartar. Under this
introduce, very carefully, half an ounce-measure of water,
holding in solution a drachm of common salt ; and again,
under both these, two ounce-measures of sulphuric acid, which
has been diluted with an equal weight of water, and allowed
to become cool. The introduction of a second and third li-
* Thomson’s Annals, vii. 426.
f To prepare nitrate of copper, dissolve the filings or turnings of that
metal in a mixture of one part nitrous acid and three parts water; decant
the liquor when it has ceased to emit fumes : and evaporate it to dryness,
in a copper or earthen dish. The dry mass must be kept in a bottle.
SECT. VIII.
CHEMICAL AFFINITY, &C.
61
quid beneath the first, is best effected, by filling, with the
liquid to be introduced, the dropping tube, fig. 15. pi. i.
which may be done by the action of the mouth. The finger
is then pressed on the upper orifice of the tube ; and the lower
orifice, being brought to the bottom of the vessel containing
the liquid, the finger is withdrawn, and the liquid descends
from the tube, without mingling with the upper stratum.
When a solution of carbonate of potash is thus separated from
diluted sulphuric acid, for which it has a powerful affinity, by
the intervention of a thin stratum of brine, the two fluids will
remain distinct and inefficient on each other ; but, on stirring
the mixture, a violent effervescence ensues, in consequence of
the action of the sulphuric acid on the potash.
X. Two bodies , having no affinity for each other , unite by the
intervention of a third. — Thus, the oil and water which, in Ex¬
periment I., could not, by agitation, be brought into union,
unite immediately on adding a solution of caustic potash. The
alkali, in this case, acts as an intermedium. The fact, indeed,
admits of being explained by the supposition, that the oil and
alkali form, in the first instance, a compound which is soluble
in water.
XI. Saturation and neutralization illustrated. — Water, after
having taken up as much common salt as it can dissolve, is
said to be saturated with salt. Muriatic acid, when it has
ceased to act any longer on lime, is said to be neutralized , as
is also the lime.
XII. The properties characterizing bodies , when separate , are
destroyed by chemical combination , and new properties appear in
the compound.— Thus, muriatic acid and lime, which, in a se¬
parate state, have each a most corrosive taste, lose this entirely
when mutually saturated ; the compound is extremely soluble,
though lime itself is very difficult of solution ; the acid no lon¬
ger reddens syrup of violets ; nor does the lime change it, as
before, to green. The resulting compound, also, muriate of
lime, exhibits new properties. It has an intensely bitter
taste ; is susceptible of a crystallized form ; and the crystals,
when mixed with snow or ice, generate a degree of cold suf¬
ficient to freeze quicksilver.
XIII. Single elective affinity illustrated.— I* Add to the
62
CHEMICAL AFFINITY, &C.
CHAP. II.
combination of oil with alkali, formed in Experiment X., a
little diluted sulphuric acid. The acid will seize the alkali,
and set the oil at liberty, which will rise to the top. In this
instance, the affinity of alkali for acid is greater than that of
alkali for oil. 2. To a dilute solution of muriate of lime
(prepared in Experiment II.), add a little of the solution of
pure potash. The potash will seize the muriatic acid, and the
lime will fall down, or be precipitated.
XIV. In every instance , in comparing the affinities of tvuo
bodies for a third , a weaker affinity , in one of the two compared ,
will be found to be compensated by increasing its quantity.— It is
not easy to offer clear and unequivocal examples of this law, and
such as the student may submit to the test of experiment. The
following, however, may illustrate the proposition sufficiently:
Mingle together, in a mortar, one part of muriate of soda
(common salt) with half a part of red oxide of lead (litharge,
or red lead), and add sufficient water to form a thin paste.
The oxide of lead, on examining the mixture after twenty-four
hours, will be found not to have detached the muriatic acid
from the soda; for the strong taste of that alkali will not be
apparent. Increase the weight of the oxide of lead to three
or four times that of the salt ; and, after the same interval,
the mixture will exhibit, by its taste, marks of uncombined
soda. This proves, that the larger quantity of the oxide must
have detached a considerable portion of muriatic acid from
the soda, though the oxide has a weaker affinity for that acid
than the soda possesses.
Another illustration of the same general principle has been
suggested by Berzelius. It is necessary to premise, that the
colour of the compound of sulphuric acid with oxide of cop¬
per is blue, and that of muriatic acid with the same oxide,
green. To a saturated solution of sulphate of copper in
water, add by degrees concentrated muriatic acid. Every
addition will render the colour of the liquid more distinctly
green, showing an increased production of muriate of copper ;
the oxide of copper being divided between the sulphuric and
muriatic acids, in proportion to the quantity of each acid that
is present.
XV. Double elective affinity exemplified. — In a watery solu-
SECT. VIII.
CHEMICAL AFFINITY, &C.
65
fcion of sulphate of zinc, immerse a thin sheet of lead : the lead
will remain unaltered, as also will the sulphate ol zinc, be¬
cause zinc attracts sulphuric acid more strongly than lead.
But let a solution of acetate of lead be mixed with one of sul¬
phate of zinc ; the lead will then go over to the sulphuric acid,
while the zinc passes to the acetic. The sulphate of lead being
insoluble, will fall down in the state of a white powder ; but
the acetate of zinc will remain in solution. The changes that
occur in this experiment will be better understood from the
following scheme :
Acetate of Zinc
Zinc
Acetic Acid
Sulphate
of
Zinc.
Water
at 60°
Acetate
> of
Lead
Sulphc Acid Lead
— - -
Sulphate of Lead
The vertical brackets include the original compounds, viz.
sulphate of zinc, and acetate of lead ; and the horizontal line
and bracket point out the new ones, viz . acetate of zinc and
sulphate of lead. By the upper horizontal line, it is denoted,
that the acetate of zinc remains in solution; and, by the point
of the lower bracket being directed downwards, it is meant
to express, that the sulphate of lead falls down, or is preci¬
pitated.
CHAPTER III.
OF HEAT OR CALORIC.
SECTION I.
General Observations on Heat .
When we apply the hand to a body which is hotter than
itself, we are sensible of a peculiar feeling, which we agree to
call the sensation of heat. At the same time we observe, in al¬
most all bodies that are placed in the same situation with the
hand, certain effects, the most remarkable of which is an en¬
largement of their dimensions. These circumstances, with very
few exceptions, so constantly accompany each other, that we
can have little or no hesitation in referring them to one and
the same cause. Of the nature of this cause we have no sa¬
tisfactory evidence ; and we are unable to demonstrate either
that it consists in any general quality of bodies, or that it re¬
sides in a distinct and peculiar kind of matter. The opinion,
however, which best explains the phenomena, is that which
ascribes them to an extremely subtile fluid, of so refined a na¬
ture, as to be capable of insinuating itself between the parti¬
cles of the most dense and solid bodies. To this fluid, as well
as to the sensation which it excites, the term heat was formerly
applied. But there was an obvious impropriety in confound¬
ing, under one appellation, two things so distinct as a sensa¬
tion and its cause; and the term caloric , first proposed by
Lavoisier, is now, therefore, generally adopted to denote the
cause of heat. Occasionally, however, in order to avoid too
frequent a repetition of the same word, the term heat is still
employed in a more extensive sense, to express not only the
sensation which it usually denotes, but also some of the modifi¬
cations of caloric.
Caloric, so far as its chemical agencies are concerned, may
be chiefly considered under two views — as an antagonist to
SECT. I.
OF HEAT OR, CALORIC.
the cohesive attraction of bodies — and as concurring with, and
increasing elasticity. By removing the particles of any solid
to a greater distance from each other, their cohesive attraction
is diminished; and one of the principal impediments to their
union with other bodies is overcome. On the other hand,
caloric may be infused into bodies in such quantity, as not
only to overcome cohesion, but to place their particles be¬
yond the sphere of chemical affinity. Thus, in the class of
substances called gases, the ponderable ingredient, whether
solid or liquid, is dissolved in so much caloric, that in me¬
chanical properties the gases agree with the air of our atmo¬
sphere, especially in being permanently elastic. Different bo¬
dies of this class do not, in general, unite by simple mixture.
But if, of two gases, we employ either one or both in a state
of great condensation, or compress their particles nearer to
each other by any means, the gravitating matter of both unites,
and forms a new compound. Thus hydrogen and oxygen
gases remain together in a state of mixture, for any length of
time, without combining ; but if wre force their particles into
a state of contiguity, by sudden and violent mechanical pres¬
sure, they unite and compose water. In many cases, also,
when two bodies are combined together, one of which is fixed,
and the other becomes elastic by union with caloric, we are
able, by its interposition alone, to effect their disunion.
Thus carbonate of lime gives up its carbonic acid by the mere
application of heat.
We may consider, then, all bodies in nature as subject to
the action of twro opposite forces, the mutual attraction of their
particles on the one hand, and the repulsive power of caloric
on the other; and bodies exist in the solid, liquid, or elastic
state, as one or the other of these forces prevails. Water, by
losing caloric, has its cohesion so much increased, that it as¬
sumes the solid form of ice ; adding caloric, we diminish again
its cohesion, and render it fluid; and, finally, by a still far-
I ther addition of caloric, we change it into vapour, and give it
so much elasticity, that it may be rendered capable of burst¬
ing the strongest vessels. In many liquids, the tendency to
elasticity is even so great, that they pass to the gaseous form
by the mere removal of the weight of the atmosphere.
VOL. i. f
06
OF HEAT OR CALORIC.
CHAP. Ill,
Caloric, like all other bodies, may exist in two different
states, in a state of freedom, and in a state, either of combi¬
nation or of something nearly resembling it. In the former
state, it is capable of exciting the sensation of heat, and of
producing expansion in other bodies. To this modification
the terms free or uncombined caloric , or caloric of temperature9
have been applied. By the term temperature we are to un¬
derstand the state of a body relatively to its power of exciting
the sensation of heat, and occasioning expansion ; effects
which, in all probability, bear a proportion to the quantity of
free caloric in a given space, or in a given quantity of matter.
Thus what we call a high temperature may be ascribed to the
presence of a large quantity of free caloric ; and a low tem¬
perature to that of a small quantity. We are unacquainted,
however, with the extremes of temperature ; and may com¬
pare it to a chain, of which a few of the middle links only are
exposed to our observation.
The degree of expansion produced by caloric, it will after¬
wards appear, bears a sufficient proportion to its quantity, to
afford us a means of ascertaining the latter with tolerable ac¬
curacy. In estimating temperature, indeed, our senses are
extremely imperfect : for we compare our sensations of heat,
not with any fixed or uniform standard, but with those sen¬
sations, of which we have had immediately previous expe¬
rience. The same portion of water will feel warm to a hand
removed from contact with snow, and cold to another hand,
which has been heated before the fire. To convey, therefore,
any precise notion of temperature, we are obliged to describe
the degree of expansion produced in some one body, which
has been previously agreed upon as a standard of comparison
The standard most commonly employed is a quantity of quick¬
silver, contained in a glass ball, which terminates in a long
narrow tube. This instrument, called a thermometer , is of
the most important use in acquiring and recording our know¬
ledge of the properties and laws of caloric. The thermometer,
however, it must be obvious, is no otherwise a measure of the
quantity of caloric, than as it ascertains the amount of one of
its principal effects. In this respect, it stands in much the
same predicament as the hygrometer, when considered as a
SECT. I.
OP HEAT OR CALORIC.
mean of determining the moisture of the atmosphere. This
last instrument, it may be remembered, is composed of some
substance (such as a hair or a piece of whip-cord) which is
lengthened by a moist atmosphere and contracted by a dry
one; and in a degree proportionate to the moisture or dry¬
ness. But all the information, which the hygrometer gives
us, is the degree of moisture between certain points that form
the extremities of its scale; and it is quite incompetent to
measure the absolute quantity of watery vapour in the air.
In explaining those properties and laws of caloric, which
have become known to us by means of the thermometer, it
appears a sufficiently natural division of the subject to de¬
scribe, Istly, those effects which caloric produces, without
losing its properties of exciting the sensation of heat and oc¬
casioning expansion and, 2dly, those agencies, in which
iits characteristic properties are destroyed, and in which it
ceases to be cognizable by our senses or by the thermometer.
The expansion or dilatation of bodies, it will appear, is
almost an universal effect of an increase of temperature. Its
amount, however, is not the same in all bodies, but differs
very essentially. By the same increase of temperature, li¬
quids expand more than solids, and aeriform bodies more
than either. Nor is the same quantity of expansion effected
in the same solid or liquid, by adding similar quantities of
heat; for, generally speaking, bodies expand by equal incre¬
ments of caloric, more in high than in low temperatures.
The explanation of this fact is, that the force opposing ex¬
pansion (viz. cohesion) is diminished by the interposition of
caloric between the particles of bodies : and, therefore, when
equal quantities of caloric are added in succession, the last
portions meet with less resistance to their expansive force
than the first. In gases, which are destitute of cohesion,
equal increments of heat appear, on the contrary, to be at¬
tended with precisely equal augmentations of bulk.
An important property of free caloric, the knowledge of
which has been acquired by means of the thermometer, is its
tendency to an equilibrium . W hen a heated ball of iron is
exposed to the open air, the caloric, which is accumulated in
it, flows out ; and its temperature is gradually reduced to that
f 2
68
OF HEAT OR CALORIC.
CHAP. III. ■ i
of the surrounding medium. This is owing to two distinct :
causes : the air, immediately surrounding the ball, acquires ;
part of the caloric which escapes ; and, having its bulk in¬
creased, is rendered specifically lighter and ascends. This is
succeeded by a cooler and heavier portion of air from above,
which, in its turn, is expanded and carries off* a second quan¬
tity of caloric. Hence a considerable part of the caloric,
which is lost by a heated body, is conveyed away by the
ambient air. But the refrigeration cannot be wholly ex¬
plained on this principle; for it has been long known that
heated bodies cool, though with less celerity, under the ex¬
hausted receiver of an air pump, and even in a Torricellian
vacuum.
When the phenomena accompanying the cooling of bodies
are accurately examined, it is found that a part of the caloric,
which escapes, moves through the atmosphere with immea-
sureable velocity. In an experiment of M. Pictet, no per¬
ceptible interval took place between the time at which caloric
quitted a heated body, and its reception by a thermometer at
the distance of sixty-nine feet. It appears also to move with
equal ease in all directions, and not to be at all impeded by a
strong current of air meeting it transversely. Hence it fol¬
io vvs that the propagation of caloric, in this state of rapid
movement, does not depend on any agency of the medium
through which it passes; a conclusion strengthened by the
experiments of Sir PI. Davy, who has shown that, in a re-#
ceiver exhausted to —p, the effect of radiation is three time§
greater than in an atmosphere of the ordinary density. Like
light, heat appears to be transmitted in parallel rays ; and it
has, therefore, under this modification, been called radiant
caloric.
The proportion of caloric, lost by a heated body, in these
two different ways, may be approximated by observing what
time it takes to cool, through the same number of degrees,
in air and in vacuo. By experiments of this kind, Dr.
Franklin thought he had ascertained that a body, which re¬
quires five minutes in vacuo, will cool in air, through the
same number of degrees, in two minutes. Count Rumford’s
experiments with a Torricellian vacuum give the proportions
I
I SECT. r. OF HEAT OR CALORIC. 69
of 5 to 3. It will, perhaps, not be very remote from the
i truth, if it be stated, in general terms, that one half of the
; caloric, lost by a heated body, escapes by radiation, and that
! the rest is carried off by the ambient atmosphere.
The radiation of caloric appears to bear a proportion to
I the elevation of temperature of a body above that of the sur¬
rounding medium. Hence in part it is, that a heated body,
I during refrigeration, loses unequal quantities of caloric in
equal times. The series appears to be pretty nearly a geo-
i metrical one. Thus, supposing the temperature of a body to
! be 1000 degrees above the surrounding medium,
! In the first minute it will lose of its heat or 900°
I In the second . . . • • -to the remainder = 90
i In the third . . . T%- of 10 . . = 9
This law of refrigeration, it is asserted by Dr. Delaroche,
though nearly accurate at low temperatures, is far from being
so at high ones.
The movement of caloric by radiation occurs only in free
space, or through transparent media. But caloric is capable,
also, of passing through dense and opaque bodies, though with
prodigiously impaired velocity. Thus a long bar of iron,
heated at one end, requires considerable time to become hot
at the other. This property in bodies has been called their
conducting power, and it exists, in different bodies, in
very different degrees. It is not, however, found to bear a
proportion to any other quality of bodies.
All the properties of caloric, which have been hitherto de¬
scribed, belong to it when in a free or uncombined form : for
it continues to produce the sensation of heat and to expand
the mercury of the thermometer. In the instances of its
agency, also, that have been mentioned, no permanent change
of form or of properties is effected in the bodies which have
imbibed caloric. A bar of iron, after being expanded by
heat, returns on cooling to the same state as before, and ex¬
hibits all its former qualities. In certain cases, however,
caloric is absorbed by bodies, with the loss of its distinguish¬
ing properties. It can then be no longer discovered by our
70
OF HEAT OR CALORIC.
CHAP. III.
senses or by the thermometer : and it produces important and
sometimes permanent changes in the bodies into which it
enters.
Those effects of caloric, in the production of which it loses
its distinguishing properties, may be classed under two gene¬
ral heads.
I. All bodies , in passing from a denser to a rarer state , absorb
caloric. — Thus solids, during liquefaction, imbibe a quantity
of caloric, which ceases to be apparent to our senses or to the
thermometer: or, as it has been termed, becomes latent. In
a similar manner, solids and liquids, during their conversion
into vapours or gases, render latent a quantity of caloric,
which is essential to the elasticity of the new product. In
common language cold is, in such cases, said to be produced;
but by the production of cold we are to understand, in philo¬
sophical language, nothing more than the passage of caloric
from a free to a latent form.
II. All bodies , by an increase of density , evolve or give out
caloric , which passes from a latent to a free state. — The simplest
illustration of this law is in the effect of hammering a piece of
metal, which may thus be intensely heated, while ail that is
effected is an augmentation of its density. Liquids by be¬
coming solids, or gases by conversion into liquids, also, evolve
caloric, or produce an increase of temperature. A pound of
water, condensed from steam, will render 100 pounds of
water at 50° warmer by 11°; whereas a pound of boiling
water will produce the same rise of temperature in no more
than about 13^- pounds. This is owing to the much greater
quantity of caloric, existing in a pound of steam, than in a
pound of boiling water, though steam and boiling water affect
the thermometer in precisely the same degree.
It is a question which has excited considerable interest
among philosophers, whether caloric, when thus absorbed
and rendered latent, enters into chemical combination, or is
merely united by the same kind of ti s as that portion of ca¬
loric that produces the temperature of bodies. Does ice, for
example, when changed into water, form a chemical union
with aloric, similar to that which exists between potash and
sulphuric acid ? Such appears to have been the opinion of
4
I SECT. I. OF HEAT OR CALORIC. */l
! Dr. Black, who, by the powers of an original and well-di¬
rected genius, discovered the greater number of those facts
that form the groundwork of the theory of latent heat. The
| resemblance, however, between chemical union and the dis¬
appearance of caloric, which, on first view, appears extremely
; striking, will be found, it must be confessed, less close on a
nearer examination. For caloric may be made to quit those
bodies, into which it has entered with the loss of its peculiar
; properties, merely by reducing their temperature; whereas
chemical combinations in general cannot be destroyed, ex
: cept by the interference of more energetic affinities. In op -
| position to the foregoing theory, it has been contended that
I the absorption of caloric by bodies is a consequence of what
has been called a change of their capacity . Thus ice, it is
supposed, in becoming water, has its capacity for caloric in¬
creased, and the absorption of caloric is a consequence of this
increased capacity. This theory, however, is deficient, inas¬
much as it fails to explain what is the cause of that change of
form, which is assumed to account for the increase of capa¬
city. Notwithstanding this obvious objection, I have retained
the term capacity to express, in the abstract, that power by
which bodies absorb and render latent different quantities of
caloric ; or the property of requiring more or less caloric for
raising their temperature an equal number of degrees. The
absorption of caloric, then, will always be owing to an in¬
crease, and its evolution to a decrease, of capacity. The use
of these terms may be exemplified by a slight change of the
perspicuous language of Dr. Crawford. 44 The capacity for
containing caloric*,” he observes, 44 and the absolute caloric
contained, are distinguished as a force from the subject upon
which it operates. When we speak of the capacity , we mean
a power inherent in the heated body ; when we speak of the
absolute caloric , we mean an unknown principle, which is re¬
tained in the body by the possession of this power ; and when
we speak of the temperature , we consider the unknown prin¬
ciple as producing certain effects upon the thermometer.”
As the capacities of bodies determine their absolute quan-
* Dr. Crawford on Heat, p. 8.
72
OF HEAT OR CALORIC.
CHAP. III.
tities of caloric, it seems reasonable to conclude, that if we can
ascertain how much caloric a body absorbs or gives out in
changing its form, and in what proportion its capacity is at
the same time altered, we may deduce the absolute quantity of
heat which it contains. Now it will be afterwards shown that
the heat, evolved by water in freezing, is equal to 140°; and
the capacity of water has been stated to bear to that of ice the
proportion of 10 to 9. Water, then, in becoming ice, must
give out -Y^th of its whole caloric, and as this amounts to 140°,
ten times 140 (or 1400°) is the whole quantity of caloric in
water at the temperature of 32°: and deducting 140 from
1400, we have 1260° for the caloric contained in the ice it¬
self, This method of determining the problem appears, how¬
ever, to me, to be liable to several objections, which it would
take up too much room to state in this place, and which I
have elsewhere urged at considerable length*.
These general observations I have deemed it necessary to
make, with a view of connecting together the propositions
respecting caloric, and the experiments illustrating them, that
form the subject of the following sections. The inquiry re¬
specting heat is one which presents a boundless field for in¬
teresting speculation ; and it would have been easy to have
extended very considerably the discussion of its nature and
properties. But in this work, I have no farther object than
to lead the student, by easy steps, to a knowledge of what
has been actually determined by experiment, or strictly and
legitimately deduced from it.
SECTION II.
Illustrations of the Effects of Free Caloric .
I. Caloric expands all bodies :■ — The expansion of liquids is
shown by that ol the mercury of a thermometer, or by im¬
mersing in hot water a glass matrass (pi. i. fig. 4), filled, up
to a mark in the neck, with spirit of wine, tinged with any
* Manchester Memoirs, v. j or Phil, Mag,
: SECT. II.
EFFECTS OF FREE CALORIC.
73
colouring substance. The spirit expands immediately when
; heated, and would overflow if not placed in a cooler situation.
| The degree of expansion produced in different liquids, by
ij similar elevations of temperature, varies very considerably.
' Thus, water expands much more than mercury, and alcohol
i more than water. This difference of expansibility is even
; sufficiently striking to appear in a remarkable degree, when
j we immerse, in water heated to 150°, three equal glass vessels
: of the shape of thermometer tubes, containing the one mer-
: cury, the other water, and the third spirit of wine. The
; spirit will begin to escape from the aperture of the vessel,
j before the mercury has ascended far in the stem*. The ex-
j pansion of aeriform bodies is shown, by holding, near the fire,
\ a bladder filled with air, the neck of which is closely tied, so
i as to prevent the enclosed air from escaping. The bladder
r will soon be fully distended, and may even be burst by con¬
tinuing and increasing the heat. All aeriform bodies undergo
the same expansion by the same additions of heat, or part
of their bulk for each degree of Fahrenheit’s thermometer,
between the freezing and boiling points. The expansion of
solids is evinced, by heating a rod of iron, ol such a length
as to be included, when cold, between two points, and the
diameter of which is such, as barely to allow it to pass through
an iron ring. When heated, it will have become sensibly
longer ; and it will be found incapable of passing through the
ring. This property of metals has been applied to the con¬
struction of an instrument for measuring temperature, called
a pyrometer , a neat and distinct representation of which is
given in the first volume of “ Chemical Conversations;” and
also, by M. Breguet, to the formation of a very sensible me¬
tallic thermometer f .
The degree of expansion is not the same for all solids, and
even differs materially in substances of the same class. Thus,
the metals expand in the following order, the most expansible
being placed first; zinc, lead, tin, copper, bismuth, iron, steel,
antimony, palladium, platinaj.
* See a table of the expansion of liquids in the Appendix.
f Ann. de China, et Phys. v. 312.
% See the table in the Appendix.
74
OF HEAT OR CALORIC.
CHAP. III.
All the above bodies return again, on cooling, to their
former dimensions.
II. Construction of the thermometer founded on the principle *
of expansion, — The thermometer is an instrument of so much
importance, that it may be expedient to explain the construc¬
tion of the different kinds which are required in chemical re¬
searches.
The instrument employed by Sanctorio, to whom the in¬
vention of the thermometer is generally ascribed, was of a very
simple kind, and measured variations of temperature by the
variable expansion of a confined portion of air. To prepare
this instrument, a glass tube (pi. i. fig. 9) is to be provided,
eighteen inches long, open at one end, and blown into a ball
at the other. On applying a warm hand to the ball, the in¬
cluded air expands, and a portion is expelled through the
open end of the tube. In this state, the aperture is quickly
immersed in a cup filled with any coloured liquid, which
ascends into the tube, as the air in the ball contracts by cooling.
The instrument is now prepared. An increase of temperature
forces the liquor down the tube; and, on the contrary, the
application of cold causes its ascent. These effects may be
exhibited, by alternately applying the hand to the ball, and
then blowing on it with a pair of bellows. By the application
of a graduated scale, the amount of the expansion may be
measured.
The ball of the above instrument, it must be obvious, cannot
be conveniently applied to measure the temperature of liquids.
For adapting it to this purpose, a slight variation may be
made in its construction, as represented fig. 8, a . To prepare
this instrument, a small spherical glass vessel is to be about
one 6th or one 4th filled with any coloured liquid. The tube,
open at both ends, is then to be cemented into the neck, with
its lower aperture beneath the surface of the fluid. The ex¬
pansion of the included air drives the liquid up the stem, to
which we may affix a graduated scale, corresponding with that
of a common mercurial thermometer. Other modifications
have also been made by different philosophers. One of the most
useful and simple forms is represented fig. 8, b. It consists
merely of a tube of very small bore, from 9 to 1 2 inches long.
|
li
SECT. II. CONSTRUCTION OF THERMOMETERS. 75
at one end of which is blown a bah, from half an inch to an
inch in diameter, which is afterwards blackened by paint, or
by the smoke of a candle. A small column of coloured liquid,
about an inch in length, is then introduced, by a manipula¬
tion similar to that already described. To fit the instrument
for use, this column ought to be stationary, about the middle
of the tube, at the common temperature of the atmosphere.
The slightest variation of temperature occasions the move-
i ment of the coloured liquid ; and a scale of equal parts mea¬
sures the amount of the effect.
An insuperable objection, however, to the air thermometer,
i as thus constructed, is, that it is affected, not only by changes
of temperature, but by variations of atmospheric pressure. Its *
utility consists in the great amount of the expansion of air,
which, by a given elevation of temperature, is increased in
bulk above twenty times more than mercury. Hence it is
adapted to detect minute changes of temperature, which the
mercurial thermometer would scarcely discover.
An important modification of the air thermometer has been
invented by Mr. Leslie, and employed by him, with great
advantage, in his interesting researches respecting heat. To
this instrument he has given the name of, the Differential
Thermometer. Its construction is as follows: “ Two glass
tubes of unequal length, each terminating in a hollow ball,
and having their bores somewhat widened at the other ends (a
small portion of sulphuric acid, tinged with carmine, being
introduced into the ball of the longer tube), are joined toge¬
ther by the flame of a blow-pipe, and afterwards bent nearly
into the shape of the letter U (see fig. 7), the one flexure
being made just below the joining, where the small cavity
facilitates the adjustment of the instrument. This, by a little
dexterity, is performed, by forcing, with the heat of the hand,
a few minute globules of air from the one cavity into the other.
The balls are blown as equal as the eye can judge, and from
four iOths to seven lOths of an inch diameter. The tubes are
such as are drawn for thermometers, only with wider bores ;
that of the short one, to which the scale is affixed, must have
an exact calibre of a 50th, or a doth, of an inch. The bore
of the long tube need not be so regular, but should be visibly
76
OF HEAT OR CALORIC.
CHAP. Ill*
larger, as the coloured liquid will then move quicker under
any impression. Each leg of the instrument is from three to
six inches in height, and the balls are from two to four inches
apart.
44 A moment’s attention to the construction of this instru-
ment will satisfy us, that it is affected only by the difference of
heat in the corresponding balls; and is calculated to measure
such difference with peculiar nicety. As long as both balls
are of the same temperature, whatever this may be, the air
contained in both will have the same elasticity, and, conse¬
quently, the intercluded coloured liquor, being pressed equally
in opposite directions, must remain stationary. But if, for
instance, the ball which holds a portion of the liquor be
warmer than the other, the superior elasticity of the confined
air will drive the liquid forwards, and make it rise, in the
opposite branch, above the zero, to an elevation proportional
to the excess of elasticity, or of heat.” The amount of the
effect is ascertained by a graduated scale, the interval between
freezing and boiling being distinguished into 100 equal de¬
grees. This instrument, it must be obvious, cannot be ap¬
plied to measure variations in the temperature of the sur¬
rounding atmosphere, for the reason already assigned. It is
peculiarly adapted to ascertain the difference of the temper¬
atures of two contiguous spots in the same atmosphere; for
example, to determine the heat in the focus of a reflector.
Thermometers, filled with spirit of wine (a liquid which has
not been congealed by any degree of cold hitherto produced),
are best adapted to the measurement of very low temperatures,
at which mercury would freeze. The amount of the expan¬
sion of alcohol, also, which exceeds that of mercury above
eight times, fits it for ascertaining very slight variations of
temperature. But it cannot be applied to measure high de¬
grees of heat; because the conversion of the spirit into vapour
would burst the instrument.
The fluid, best adapted for filling thermometers, is mercury,
which, though it expands less in amount than air, or alcohol,
still undergoes this change to a sufficient degree; and, in con¬
sequence of its difficult conversion into vapour, may be ap¬
plied to the admeasurement of more elevated temperatures.
SECT. II.
CONSTRUCTION OF THERMOMETERS.
11
As a considerable saving of expense will accrue to the experi¬
mentalist, who is able to construct mercurial thermometers,
I shall offer some rules for this purpose. In general, however,
I should deem it preferable merely to superintend their con-
struction, and to be satisfied, by' actual inspection, that the
necessary accuracy is observed ; because much tune must be
unavoidably lost, in acquiring the manual skill which is essen¬
tial to construct them neatly.
Thermometer tubes may be had at the glass-house, and ot
various philosophical instrument makers. In purchasing them,
those should be rejected that are not hermetically sealed at
both ends; because the smallest condensation of moisture,
which must take place when air is freely admitted within the
tube, is injurious to the accuracy of the instrument. A small
bottle of elastic gum should be provided, in the side of which
a brass valve is fixed, or a piece of brass perforated by a
small hole, to be occasionally stopped by the hand. A blow¬
pipe is also an essential part of the apparatus; and, m addi¬
tion to one of the ordinary kind, it will be found usem . to
have one which is supplied with air by a pair ot double bel¬
lows, worked by the loot.
Before proceeding to the construction of the thermometer,
it is necessary to ascertain, that the tube is of equal diameter
in different parts. This is done by breaking off both ot the
sealed ends, immersing one of them an inch or two deep m
clean and dry mercury, and then closing the other end with
the fin o’er. On withdrawing the tube from toe mercury, a
small column of that fluid remains in it, the length of which
is to be examined, by laying the tube horizontally on a gra¬
duated ruler*. By inclining the tube, this column may be
gradually moved through its whole length ; and .1 the tube
be of uniform bore, it will measure the same in every part.
Such a degree of perfection, however, is scarcely ever to be
observed throughout tubes 01 considerable 1 o 1 '
general, a portion of the tube will be found pci.^ci, ' " !1,il
*• If the tube be of an extremely small bore, the mercury wTl not enter,
and must be drawn in by the action of the elastic buttle, and not by thm
mouth.
78
OF HEAT OR CALORIC.
CHAP. HE*
cient length for a thermometer, and this part is to be
broken off.
On one end of the tube let the neck of the elastic bottle be
firmly tied ; and let the other end be heated by the flame of
the blow-pipe, till the glass softens. The softened part must
then be pressed, by a clean piece of metal, into the form of a
rounded button ; and to this the flame of the lamp must be
steadily applied, till it acquires a white heat, and seems about
to enter into fusion. To prevent its falling on one side, the
tube, during this time, must be constantly turned round by
the hand. When the heated part appears perfectly soft, re¬
move it quickly from the lamp, and, holding the tube verti¬
cally, with the elastic bottle uppermost, press this last gently
with the hand. The glass will be blown into a small ball, but
not into one sufficiently thin for the purpose. To this the
flame of the lamp must again be applied, turning it quickly
round ; and, on a second or third repetition of the process
of blowing, the ball will be completely formed. The propor¬
tion of the size of the ball to the bore of the tube can only
be learned by some experience.
To fill the ball, which has been thus formed, with mercury,
the air must first be expelled by holding it over the flame of
an Argand's lamp, and then quickly immersing the open end
of the tube in very clean and dry quicksilver. As the ball
cools, the mercury will ascend, and will partly fill it. Let a
paper funnel be tied firmly over the open end of the tube ;
into this pour a small portion of quicksilver, and apply the
heat of the lamp to the ball. Any remaining portion of air
will thus be expelled ; and if the heat be raised so as to boil
the mercury, the ball and stem will be filled with mercurial
vapour, the condensation of which, on removing the ball
from the lamp, will occasion a pretty complete vacuum. Into
this vacuum, quicksilver will descend from the paper cone ;
and the instrument wall be completely filled; But for the pur¬
pose of a thermometer, it is necessary that the mercury should
rise only to a certain height of the stem ; and a few drops
may, therefore, be expelled by cautiously applying the heat
of the lamp. To estimate whether the proper quantity of
quicksilver has been left in the instrument, immerse the ball
SECT. II, CONSTRUCTION OF THERMOMETERS. 79
first in ice-cold water, and then in the mouth. The space
between these two points will comprise 63 degrees, or pretty
nearly one third of the whole space between the freezing and
boiling points of water. If the empty part of the tube ex¬
ceeds, in length, about three times the portion thus filled by
the expanded quicksilver, we may proceed (when an instru-
ment is wanted with a scale including only from 32° to 212°)
to seal it hermetically : which is done as follows : The part to
) be sealed is first heated with the blow-pipe, and drawn out
to a fine capillary tube ; the bulb is then heated, till a few par-
tides of quicksilver have fallen from the top of the tube : at
: this moment, the flame of another candle is directed, by the
blow-pipe, on the capillary part of the tube, the candle is
withdrawn from the ball, and the tube is sealed, at the instant
when the mercury begins to descend. If this operation has
been skilfully performed, so as to leave no air in the tube, the
whole of the tube should be filled with quicksilver on holding
the instrument with the ball uppermost.
To have very large degrees, the ball must bear a consider¬
able proportion to the tube ; but this extent of scale cannot
be obtained without sacrificing, in some measure, the sensibi¬
lity of the instrument. The whole of the process of construct¬
ing thermometers neatly and accurately is connected with the
possession of manual skill, which practice only can confer;
and it is scarcely possible, without the most tedious minute¬
ness, to describe all the necessary precautions and manipula¬
tions. These will readily suggest themselves to a person who
carries the above instructions into effect.
In graduating thermometers, the first step consists in taking
the two fixed points. The freezing point is ascertained, by
immersing, in thawing snow or ice,, the ball and part of the
stem ; so that the mercury, when stationary, shall barely ap¬
pear above the surface. At this place let a mark be made
with a file. In taking the boiling point, considerable caution
is required ; and, for reasons which will afterwards be stated,
attention must be paid to the state of the barometer, the
height of which, at the time, should be precisely 29*8. A
tin vessel is to be provided, (for, according to Gay Lus-
OF HEAT OR CALORIC*
CHAP. Ill,
sac*, one of glass leads to erroneous results,) four or five inches
longer than the thermometer, and furnished with a cover, in
which are two holes. Through one of these, the thermometer
stem must be passed (the bulb being within the vessel), so that
the part, at which the boiling point is expected, may be just
in sight. The other hole may be left open ; and the cover
being fixed in its place, the vessel, containing a few inches of
water at the bottom, is to be set on the fire. The thermo¬
meter will presently be wholly surrounded by steam ; and
when the mercury becomes stationary in the stem, its place
must be marked. The scale of Fahrenheit is formed by trans-
ferring the intermediate space to paper by a pair of compasses,
and dividing it into 180°, the lowest being called 82°, and the
highest 212°. The scale of other countries, however, differs
considerably ; but these variations do not prevent the com¬
parison of observations with different instruments, when the
freezing and boiling points of water are agreed upon as fixed
data. In the Appendix, rules will be given for converting the
degrees of other scales to that of Fahrenheit.
III. The dilatations and contractions of the fluid in the mer¬
curial thermometer , are nearly proportional to the quantities of
caloric , which are communicated to the same homogeneous bodies ,
or separated from them , so long as they retain the same form.
Thus a quantity of caloric, required to raise a body 20° in
temperature, by the mercurial thermometer, is nearly double
that which is required to raise it 10°. Hence there appears
to be a pretty accurate proportion between the increments or
decrements of heat, and the increments and decrements of
expansion in the mercury of a thermometer. On this prin¬
ciple, if equal quantities of hot and cold water be mixed to¬
gether, and a thermometer be immersed in the hot water, and
also in the cold, previously to the mixture, the instrument
should point, after the mixture, to the arithmetical mean, or
to half the difference of the separate heats, added to the less
or subtracted from the greater. This will be proved to be
actually the fact, by the following experiment. Mix a pound
* 82 An. de Ch. 174, and 7 An. de Ch. et Pliys. 307.
SECT, II. EATIO OF EXPANSION Si
of water at 172° with a pound at 32°. Half the excess of the
caloric of the hot water will pass to the colder portion ; that
is, the hot water will be cooled 70°, and the cold will receive
70° of temperature ; therefore 172 — 70, or 32 + 70 = 102,
will give the heat of the mixture. To attain the arithmetical
mean exactly, several precautions must be observed *4
The experiments of De Luc, however, have shown, that
the ratio of expansion does not, strictly , keep pace with the
actual increments of temperature; and that the amount of
the expansion increases with the temperature. Thus if a
given quantity of mercury, in being heated from 32 to 122°,
the first half of the scale, be expanded 14 parts, in being
raised from 122 to 212, the higher half, it will be expanded
15 parts.
From the inquiries of Mr. Dalton, it appears to follow,,
that the irregularity of the expansion of mercury is consider¬
ably greater than has been stated by De Luc* By the com¬
mon mercurial thermometer, we cannot ascertain the true rate
of expansion in quicksilver ; for it must be obvious that the
: expansion of the glass ball, in which it is contained, must
; considerably affect the result. If the capacity of the ball re-
i mained unaltered, we should then be able to determine the
: actual rate of expansion ; but by an increase of temperature
| its capacity is enlarged, and space is thus found, within the
; ball, for the expansion of that mercury, which would other¬
wise be driven into the tube. By knowing the rate of expan¬
sion in glass itself, we can correct this error; but a small
error in this datum will lead us considerably wrong as to the
r true expansion of quicksilver. The real expansion of mer-
i cury in glass is greater than the apparent , by the expansion of
n the glass itself
Making due correction for this circumstance, Mr. Dalton
;has been led to conclude from his experiments, that notwith¬
standing the apparent diversities of expansion in different
ifluids, they all actually expand according to the same law;
,;i viz. that the quantity of expansion is as the square of the tem -
Aperature from their respective freezing points , or from their
* See Crawford on Animal Heat, p. 95, &c*
1 VOL. I. &
82
OF HEAT OR CALORIC.
CHAP. III.
points of greatest density. If then a thermometer be con¬
structed, with degrees corresponding to this law, they will be
found to differ very considerably from those of the common
mercurial thermometer, in which the space between freezing
and boiling is divided into 180 equal parts. In the Appendix
will be found a table showing the correspondence between
the old scale and the new one constructed on Mr. Dalton’s
principle.
IV. Uncombined caloric has a tendency to an equilibrium. —
Any number of different bodies, at various temperatures, if
placed under similar circumstances of exposure, all acquire a
common temperature. Thus, if in an atmosphere at 60°, we
place iron filings heated to redness, boiling water, water at
32°, and various other bodies of different temperatures, they
will soon affect the thermometer in the same degree. The
same equalization of temperature is attained, though less
quickly, when a heated body is placed in the vacuum of an
air-pump. The rate of cooling in air is to that in vacuo , the
temperatures being equal, nearly as five to two.
II. Motion of Free Caloric . — 1. Its Radiation. — 2. Its Passage
through Solids and Fluids.
Caloric escapes from bodies in two different modes. — Part of
it finds its way through space, independently of other matter,
and with immeasureable velocity. In this state it has been
called, radiant heat, or radiant caloric.
Radiant caloric exhibits several interesting properties.
1. Its reflection. ( a ) Those surfaces, that reflect light most
perfectly, are not equally adapted to the reflection of caloric.
Thus, a glass mirror, which reflects - light with great effect
when held before a blazing fire, scarcely returns any heat, and
the mirror itself becomes warm. On the contrary, a polished
plate of tin, or a silver spoon, when similarly placed, reflects,
to the hand, a very sensible degree of warmth ; and the metal
itself remains cool. Metals, therefore, are much better re¬
flectors of caloric than glass ; and they possess this property*
exactly according to their degree of polish.
(b) Caloric is reflected according to the same law that re¬
gulates the reflection of light. This is proved by an interest-
SECT. II.
RADIANT CALORIC.
85
ing experiment of M. Pictet ; the means of repeating \*hich
may be attained at a moderate expense. Provide two reflec¬
tors of planished tin ( a and b9 fig. 45), which may be 12 inches
diameter, and segments of a sphere of nine inches radius.
Parabolic mirrors are still better adapted to the purpose ; but
their construction is less easy. Each of these must be fur¬
nished, on its convex side, with the means of supporting it in
a perpendicular position on a proper stand. Place the mirrors
opposite to each other on a table, at the distance of from six
to 12 feet. Or they may be placed in a horizontal position, as
represented in the fourth plate to Sir H. Davy’s Chemical
Philosophy, an arrangement in some respects more convenient.
In the focus of one, let the ball of an air thermometer, c, or
(which is still better) one of the balls of a differential ther¬
mometer, be situated; and in that of the other, suspend a
ball of iron, about four ounces in weight, and heated below
ignition, or a small matrass of hot water, d; having previously
interposed a screen before the thermometer. Immediately on
withdrawing the screen, the depression of the column of
liquid, in the air thermometer, evinces an increase of tem¬
perature in the instrument. In this experiment, the caloric
flows first from the heated ball to the nearest reflector ; from
this it is transmitted, in parallel rays, to the surface of the
second reflector, by which it is collected into a focus on the
instrument. This is precisely the course that is followed by
radiant light ; for if the flame of a taper be substituted for the
iron ball, the image of the candle will appear precisely on that
spot (a sheet of paper being presented for its reception) where
the rays of caloric were before concentrated.
(c) When a glass vessel, filled with ice or snow, is substi¬
tuted for the heated ball, the course of the coloured liquid in
the thermometer will be precisely in the opposite direction ;
for its ascent will show, that the air in the ball is cooled by this
arrangement. This experiment, which appears, at first view,
to indicate the reflection of cold, presents, in fact, only the
reflection of heat in an opposite direction ; the ball of the
thermometer being, in this instance, the hotter body. 44 And
since heat emanates from bodies in quantities greater as their
temperature is higher, the introduction of a cold body into
OP HEAT OR CALORIC.
CHAP. Mr
84
the focus of one mirror, necessarily diminishes the tempera¬
ture of a thermometer in the focus of the other, in the same
manner as a black body placed in the focus of the one, would
diminish the quantity of light in the focus of the other
(d) In Mr. Leslie’s 66 Enquiry into the Nature, &c. of
Heat,” a variety of important experiments are detailed, which
show the influence of covering the reflectors with various sub¬
stances, or of mechanically changing the nature of their sur«
faces, on their power of returning caloric.
2. Caloric is refracted , also, according to the same law that
regulates the refraction of light. This interesting discovery
we owe to Dr. Herschell, whose experiments and apparatus,
however, cannot be understood without the assistance of a
plate. For this reason, I refer to his paper in the 90th vol.
of the Philosophical Transactions, or in the 7th vol. of the
Philosophical Magazine.
3. The nature of the surface of bodies has an important in¬
fluence over their power of radiating caloric.
To exhibit this influence experimentally, let a canister of
planished block tin, forming a cube of six or eight inches, be
provided, having an orifice at the middle of its upper side,
from half an inch to an inch diameter, and the same in height.
This orifice is intended to receive a cap having a small hole,
through which a thermometer is inserted, so that its bulb may
reach the centre of the canister. Let one side of the canister
be covered with black paint; destroy the polish of another
side, by scratching it with sand-paper ; tarnish a third with
quicksilver ; and leave the fourth bright. Then fill the vessel
with boiling water. The radiation of caloric from the black¬
ened side is so much more abundant than from the others, as
to be even sensible to the hand. Place it before a reflector
(fig. 45), in lieu of the heated iron ball already described.
The thermometer, in the focus of the second reflector, will
indicate the highest temperature, or most copious radiation of
caloric, when the blackened side is presented to the reflectory
less when the tarnished or scratched side is turned towards it ;
and least of all from the polished side.
* Davy's Chem. Philos, p. 206.
SECT. II.
■RADIANT CALORIC.
85
These varieties in the radiating power of different surfaces,
are attended, as might be expected, with corresponding varia¬
tions in the rate of cooling . If water in a tin vessel, all of
whose sides are polished, cools through a given number of
degrees in eighty-one minutes, it will descend through the
same number in seventy-two minutes, if the surface be tar¬
nished with quicksilver. Water, also, enclosed in a clean and
polished tin ball, cools about twice more slowly than water in
the same ball covered with oiled paper. Blackening the sur¬
face with paint, or even a thin coat of varnish, on the same
principle, accelerates greatly the rate of cooling. These facts
teach us, that vessels, in which fluids are to be long kept hot,
should have their surfaces brightly polished ; and they explain,
among other things, the superiority of metallic tea-pots over
those of earthen ware.
5. Radiant caloric is absorbed with different facility by dif¬
ferent surfaces. This is only stating, in other terms, that sur-
! faces are endowed with various powers of reflecting caloric $
! since the power of absorbing caloric is precisely opposite to
I that of reflecting it. Hence the best reflectors of heat will
absorb the least. It may be proper, however, to offer some
I illustrations of the principle under this form.
(a) Expose the bulb of a sensible thermometer to the direct
!rays of the sun. On a hot summer’s day it will probably rise,
in this climate, to 108° *. Cover it with Indian ink, and
again expose it in a similar manner. During the evaporation
of the moisture it will fall ; but as soon as the coating becomes
dry, it will ascend to 118°, or upwards, of Fahrenheit, or 10°
higher than when uncovered with the pigment. This cannot
( be explained, by supposing that the black coating is gifted
y with the power of retaining caloric, and preventing its escape;
: because, from experiments already related, it appears, that a
similar coating accelerates the cooling of a body to which it
is applied.
(b) Colour has considerable influence over the absorption
( of caloric. This is shown by the following very simple experi-
n ment of Dr. Franklin.
* Watson's Essays, v. 193.
86
OF HEAT OR CALORIC.
CHAP. III.
On a winter’s day, when the ground is covered with snow*
take four pieces of woollen cloth, of equal dimensions but of
different colours, viz . black, blue, brown, and white, and lay
them on the surface of the snow, in the immediate neighbour¬
hood of each other. In a few hours, the black cloth will have
sunk considerably below the surface; the blue almost as much;
the brown evidently less ; and the white will remain precisely
in its former situation. Thus it appears, that the sun’s rays
are absorbed by the dark coloured cloth, and excite such a
durable heat, as to melt the snow underneath ; but they have
not the power of penetrating the wThite. Hence the prefer¬
ence, generally given to dark coloured cloths during the win¬
ter season, and to light coloured ones in summer, appears to
be founded on reason.
(c) This experiment has been varied by Sir H. Davy, in a
manner which may be repeated at any season of the year.
Take six similar pieces of sheet copper, each about an inch
square, and colour the one white, another yellow, a third red,
the fourth green, the fifth blue, and the sixth black. On the
centre of one side of each piece, put a small portion of a mix¬
ture of oil and wax, or cerate, which melts at about 76°.
Then expose their coloured surfaces, under precisely equal
circumstances, to the direct rays of the sun. The cerate on
the black plate will begin to melt perceptibly before the red ;
the blue next ; then the green and the red ; and, lastly, the
yellow. The white will scarcely be affected, when the black
is in complete fusion.
Caloric passes, also, but much more slowly, through solid
and liquid bodies, which are then termed conductors of
caloric.
1. Solid bodies convey heat in all directions, upwards,
downwards, and laterally; as may be shown, by heating the
middle of an iron rod, and holding it in different directions.
2. Some bodies conduct caloric much more quickly than
others. Coat two rods, of equal length and thickness, the one
of glass, the other of iron, with wax, at one end of each only j
and then apply heat to the uncoated ends. The wax will be
melted vastly sooner from the end of the iron rod, than from
CONDUCTORS OF CALORIC.
SECT. II.
87
the glass one; which shows, that iron conducts heat more
quickly than glass.
Even the different metals possess very different powers of
conducting caloric. An approximation to the degree in which
they possess this property, may be attained by the following
method, originally employed by Dr. Ingenhouz. Procure se¬
veral solid cylinders, or rods, of the same size and shape, but
of different metals. They may be six inches long, and one
4th of an inch in diameter. Coat them, within about an inch
of one end, with bees-wax, by dipping them into this sub¬
stance when melted, and allowing the covering to congeal.
Let an iron heater be provided, in which small holes have
been drilled, that exactly receive the clean ends of the cylin¬
ders. After heating it below ignition, insert the cylinders in
their places. The conducting power may be estimated by the
length of wax coating melted from each in a given time. Ac¬
cording to the experiments of Dr. Ingenhouz, the metals may
be arranged in the following order : Silver possesses the high¬
est conducting power ; next gold ; then copper and tin, which
are nearly equal ; and, below these, platina, iron, steel, and
lead, which are greatly inferior to the rest.
It is chiefly owing to the different conducting powers of
bodies, that they affect us, when we touch them, with different
sensations of cold. Thus, if we apply the hand in succession
to a number of bodies (as a piece of wood, another of marble*
&c.), they appear cold in very different degrees. And as this
sensation is occasioned by the passage of caloric out of the
hand into the body which it touches, that body will feel the
coldest, which carries away heat the most quickly ; or which,
in other words, is the best conductor. For the same reason,
of two bodies which are heated to the same degree, and both
considerably above the hand, the best conductor is the hottest
to the touch. Thus the money in our pockets often feels hot¬
ter than the clothes which contain it.
3. Liquid and aeriform bodies convey heat on a different
principle from that observed in solids, viz. by an actual change
in the situation of their particles. That portion of the fluid,
which is nearest to the source of heat, is expanded, and be¬
coming specifically lighter, ascends, and is replaced by a
88
OF HEAT OR CALORIC.
CHAP. III.
colder portion from above. This, in its turn, becomes heated
and dilated, and gives away to a second colder portion ; and
thus the process goes on, as long as the fluid is capable of im¬
bibing heat.
(<2) Take a glass tube, eight or 10 inches long, and about
an inch in diameter. Pour into the bottom part, for about the
depth of an inch, a little water tinged with litmus, and then
fill up the tube with common water, pouring on the latter ex¬
tremely gently, so as to keep the two strata quite distinct. If
the upper part of the tube be first heated, the coloured liquor
will remain at the bottom ; but if the tube be afterwards heated
at the bottom, the infusion will ascend, and will tinge the
whole mass of fluid.
( b ) Into a cylindrical glass jar, four inches diameter, and
12 or 14 deep, let a circular piece of ice be fitted 3± inches
thick, and of rather less diameter than the jar. Or water may
be poured into the jar to the depth of 3~ inches, and allowed
to congeal by exposure to a freezing atmosphere, or by sur¬
rounding it with a mixture of snow and salt. The ice is to
be secured in its place by two slips of wood, crossing each
other like two diameters of a circle, set at right angles to each
other. Pour, over the cake of ice, water of 32° temperature,
to the depth of twro inches ; and on its surface let there float a
shallow circular wooden box, perforated with holes. From
the cock of a tea-urn, filled with boiling water, and raised so
that its spout may be above the top of the jar, suspend a num¬
ber of moistened threads, the lower ends of which must rest
on the surface of the box. By this arrangement, when the
cock is turned, the hot water will trickle down the threads,
and will have its fall considerably broken. It will then spread
over the surface of the box, and pass through the perforated
holes to the cold wTater beneath, over which it will float with¬
out mixing with it. Let the jar be thus completely filled with
hot water. The ice will remain unmelted for several hours at
the bottom of the vessel.
(c) Fill a similar jar with hot water ; and, having provided*
a cake of ice, of equal size with the former one, let it be
placed on the surface of the water. I11 about three minutes,,
the whole will be melted. Both these experiments are more
£ECT. II.
CONDUCTORS OF CALORIC.
89
striking, if the water, used for forming the cakes of ice, be
previously coloured with litmus ; for, in the latter experi¬
ment, the descending currents of cold water are thus made ap¬
parent.
(d) These experiments may be varied, by freezing, in the
bottom of a tube one inch wide, a portion of water, about two
inches in depth. Then fill the tube with water of the com¬
mon temperature, and hold it inclined over an Argand s lamp,
so that the upper portion only of the tube may be heated.
When thus disposed, the water may be made to boil violently
at the surface, and yet the ice will not be melted. But if the
experiments be reversed, and (the ice floating on the surface)
heat be applied to the bottom ol the tube, the ice will be lique¬
fied in a few seconds.
(i e ) Substituting water of the temperature of 41° for the boil¬
ing water used in experiment (c), Count Rumford found, that,
in a given time, a much greater quantity of ice was melted
by the cooler water. This appears, on first view, rather para-
i doxical. The fact, however, is explained by a remarkable
i property of water, viz. that when cooled below 40° it ceases
i to contract, . and experiences, on the contrary, an enlargement
of bulk. Water, therefore, at 40° (at the bottom of which is
a mass of ice at 32°), is cooled by contact with the ice, and is
expanded at the same moment. It therefore ascends, and is
replaced by a heavier and warmer portion from above.
It is a consequence of the same property that the surface of
a deep lake is sometimes covered with ice, even when the water
below is only cooled to 40° ; for the superficial water is speci¬
fically lighter than the warmer water beneath it, and retains
its place, till it is changed into ice. This property of water
• is one of the most remarkable exceptions to the law, that
t bodies are expanded by an increase, and contracted by a di-
J minution, of temperature.
From these facts, Count Rumford concluded, that water is
a perfect non-conductor of caloric, and that it propagates ca-
r loric in one direction, viz. upwards, in consequence of the
motions which it occasions among the particles of the fluid.
The Count inferred also, that if these motions could be sus¬
pended, caloric would cease to pass through water ; and, with
90
OF HEAT OR CALORIC.
CHAP. III.
the view of deciding this question, he made the following ex¬
periments, which admit of being easily repeated. A cylin¬
drical tin vessel must previously be provided, two inches in
diameter, and 2-L inches deep, having a moveable cover, per¬
forated with a small aperture, for transmitting the stem of a
thermometer, which is to be inserted so that its bulb may
occupy the centre of the vessel.
( f) Fill this vessel with water of the temperature of the
atmosphere ; let the cover be put in its place ; and let the whole
apparatus, except the scale of the thermometer, be immersed
in water, which is to be kept boiling over a lamp. Observe
how long a time is required to raise the water from its tempe¬
rature at the outset to 180°, and remove it from its situation.
Note, also, how long it takes to return to its former tempe¬
rature.
(g) Repeat the experiment, having previously dissolved in
the water 200 grains of common starch. The thermometer
will now require about half as long again to arrive at the same
temperature. A similar retardation, and to a greater amount,
is produced by the mixture of eider-down, cotton- wool, and
various other substances, which are not chemically soluble in
water, and which can diminish its conducting power in no
other way than by obstructing the motion of its particles.
This inference, however, respecting the complete non-con¬
ducting power of water, has been set aside by the subsequent
inquiries of Dr. Thomson and Dr. Murray, especially by a
most decisive experiment of the latter. To establish the con¬
ducting power of water, it was justly deemed indispensable,
that caloric should be proved to be propagated through that
fluid downwards. This, on actual trial, it appeared to be ;
but it was objected, that the sides of the containing vessel
might be the conductor. To obviate this objection, Dr.
Murray contrived to congeal water into the form of ajar, ca¬
pable of holding liquids. This was separately filled with lin¬
seed oil and with mercury. At a proper distance below the
surface, the bulb of a thermometer was placed ; and on the
surface of the liquid rested a flat iron vessel, containing boil¬
ing water. Under these circumstances, the thermometer in¬
variably rose ; and though it ascended only a very few degrees,
6
SECT. Ill®
CALORIC THE CAUSE OF FLUIDITY.
91
yet it must be recollected, that the cooling power of the sides
of the vessel would effectually prevent any considerable eleva¬
tion of temperature. This experiment, in conjunction with
others, decisively proves, that water is a conductor, though a
slow or imperfect one, of caloric.
SECTION III.
Caloric the Cause of Fluidity .
I. The temperature of melting snow , or of thawing ice , is uni¬
formly the same at all times , and in all places. — This may be
ascertained by the thermometer, which will always, when im¬
mersed in liquefying ice or snow, point to 32° of Fahrenheit,
whatsoever may be the height of the barometer, or the ele¬
vation, above the sea, of the place where the experiment is
made #.
II. The sensible heat , or temperature of ice , is not changed by
liquefaction. — A thermometer in pounded ice stands at 32°,
and at the very same point in the water which results from
the liquefaction of ice.
III. Yet ice , during liquefaction , must absorb much caloric. —
[ Expose a pound of water at 32°, and a pound of ice at 32°, in
a room, the temperature of which is several degrees above the
1 freezing point, and uniformly the same during the experi¬
ment. The water will arrive at the temperature of the room,
i several hours before the ice is melted ; and the melted ice will
; have, as before its liquefaction, the temperature of 32°. Yet
1 the ice must, during the whole of this time, have been imbib- ,
r ing caloric, because (according to Experiment IV. § 2.) a
3 colder body can never be in contact with a warmer one, with-
i out receiving caloric from it. The caloric, therefore, which
» has entered the ice, but is not to be found in it by the ther¬
mometer, is said to have become latent. As it is the cause of
f the liquefaction of the ice, it is sometimes called caloric of
i fluidity.
IV. The quantity of caloric that enters into a pound of ice9
* Shuckburgh, Philosophical Transactions, lxix.
OF HEAT OR CALORIC®
chap. nr.
and becomes latent, during liquefaction , may be learned by expe¬
riment. — To a pound of water, at 172°, add a pound of ice at
32°. The temperature will not be the arithmetical mean
(202°), but much below it, viz. 32°. All the excess of caloric
in the hot water has therefore disappeared. From 172° take
32°; the remainder, 140°, shows the quantity of caloric that
enters into a pound of ice during liquefaction ; that is, as
much caloric is absorbed by a pound of ice, during its con¬
version into water, as would raise a pound of water from 32°
to 172°
It is from the property of its uniformly absorbing the same
quantity of caloric for conversion into water, that ice has been
ingeniously applied, by Lavoisier and Laplace, to the admea¬
surement of the heat, evolved in certain operations. Let us
suppose the body (from which the caloric, evolved either by
simple cooling or combustion, is to be measured) to be inclosed
in a hollow sphere of ice, with an opening at the bottom.
When thus placed, the heat which is given out, will be all
employed in melting the ice ; and will produce this effect in
direct proportion to its quantity. Hence the quantity of ice,
which is converted into water, will be an accurate measure of
the caloric, that is separated from the body submitted to ex¬
periment. In this way, Lavoisier ascertained that equal
weights of different combustible bodies melt, by burning, very
different weights of ice. The apparatus which he employed
for this purpose, he has called the calorimeter . Its construc¬
tion can scarcely be understood without the plate, which ac¬
companies the description in his “ Elements of Chemisty;’*
and I consider it unnecessary to copy it into this work, be¬
cause the instrument is liable to several causes of inaccuracy.
Y. Other examples of the absorption of caloric , during the
liquefaction of bodies , are furnished by the mixture of snow and
nitric acid, or of snow and common salt, both of which, in
common language, produce intense cold.
1. Dilute a portion of nitric acid with an equal weight of
water ; and, when the mixture has cooled, add to it a quan¬
tity of light fresh-fallen snow. On immersing the thermo¬
meter in the mixture, a very considerable reduction of tem¬
perature will be observed. This is owing to the absorption.
IECT. III. CALORIC THE CAUSE OF FLUIDITY.
and intimate fixation, of the free caloric of the mixture, by
the liquefying snow.
2. Mix quickly together equal weights of fresh-fallen snow
at 32°, and of common salt cooled, by exposure to a freezing
atmosphere, down to 32°. The two solid bodies, on admix¬
ture, will rapidly liquefy ; and the thermometer will sink 32°*
or to 0; or, according to Sir C. Blagden, to 4° lower*. To
understand this experiment, it must be recollected, that the
snow and salt, though at the freezing temperature of water^
have each a considerable portion of uncombined caloric.
Now salt has a strong affinity for water ; but the union cannot
take place while the water continues solid. In order, there¬
fore, to act on the salt, the snow absorbs all the free caloric
required for its liquefaction ,• and during this change, the free
caloric, both of the snow and of the salt, amounting to 32°„
becomes latent, and is concealed in the solution. This solu¬
tion remains in a liquid state at 0, or 4° below 0 of Fahren¬
heit ; but if a greater degree of cold be applied to it, the salt
separates in a concrete form.
3. Most neutral salts, also, during solution in water absorb
much caloric ; and the cold, thus generated, is so intense as
to freeze water, and even to congeal mercury. The former
experiment, however {viz. the congelation of water), may
easily be repeated on a summer’s day. Add to 32 drachms
of water, 11 drachms of muriate of ammonia, 10 of nitrate
of potash, and 16 of sulphate of soda, all finely powdered.
The salts may be dissolved separately, in the order set down.
A thermometer, put into the solution, will show, that the
cold produced is at or below freezing ; and a little water, in
a thin glass tube, being immersed in the solution, will be
frozen in a few minutes. Various other freezing mixtures are
described in Mr. Walker’s papers in the Philosophical Trans¬
actions for 1787, 88, 89, 95, and 1801. Of these the table,
given in the Appendix, for which I am indebted to the obliging
communication of the author, contains an arranged abstract.
4. Crystallized muriate of lime, when mixed with snow,
produces a most intense degree of cold. This property was
* Philosophical Transactions, Ixxviii. 281.
94 OF HEAT OR CALORIC. CHAP. II L
discovered some years ago by M. Lovitz, of St. Petersburg,
and has been since applied, in this country, to the congela--
tion of mercury on a very extensive scale. The proportions
which answer best, are about equal weights of the salt finely
powdered, and of fresh-fallen and light snow. On mixing
these together, and immersing a thermometer in the mixture,
the mercury sinks with great rapidity. For measuring exactly
the cold produced, a spirit-thermometer, graduated to 50°
below 0 of Fahrenheit, or still lower, should be employed,
A few pounds of the salt are sufficient to congeal a large
mass of mercury. By means of 13 pounds of the muriate,
and an equal weight of snow, Messrs. Fepys and Allen froze
56 pounds of quicksilver into a solid mass. The mixture of
the whole quantity of salt and snow, however, was not made
at once, but part was expended in cooling the materials them¬
selves.
On a small scale it may be sufficient to employ two or three
pounds of the salt. Let a few ounces of mercury, in a very
thin glass retort, be immersed, first in a mixture of one pound
of each ; and, when this has ceased to act, let another similar
mixture be prepared. The second will never fail to congeal
the quicksilver.
In plate iv. fig. 42, a very simple and cheap apparatus is «
represented, which I have generally employed to freeze mer¬
cury. The dimensions will be given in the description of the
plates*.
The salt thus expended may be again evaporated, and crys¬
tallized for future experiments.
The reader, who wishes for farther particulars respecting
these experiments, is referred to the Philosophical Magazine?
iii. 76.
VI. On the contrary , liquids , in becoming solid , evolve or
give out caloric , or, in common language , produce heat .
1. Water, if kept perfectly free from agitation, may be
cooled down several degrees below 32Q ; but, on shaking it, it
immediately congeals, and the temperature rises to 32°.
2. Expose to the atmosphere, when at a temperature below
- - - - - - - J
* See Appendix,
SECT. III.
CALORIC THE CAUSE OF FLUIDITY.
95
freezing (for example, at 25° of Fahrenheit), two equal quan¬
tities of water, in one only of which about a fourth of its
weight of common salt has been dissolved. The saline solu¬
tion will be gradually cooled, without freezing, to 25°. The
pure water will gradually descend to 32°, and will there re¬
main stationary a considerable time before it congeals. Yet
while thus stationary, it cannot be doubted, that the pure
water is yielding caloric to the atmosphere, equally with the
saline solution : for it is impossible that a warmer body can
be surrounded by a cooler one, without imparting caloric to
the latter. The reason of this equable temperature is well
explained by Dr. Crawford. ( On Heat , p. 80.) Water, he
observes, during freezing, is acted upon by two opposite
powers: it is deprived of caloric by exposure to a medium,
whose temperature is below 32° ; and it is supplied with ca¬
loric, by the evolution of that principle from itself, viz. of
that portion which constituted its fluidity. As these powers
are exactly equal, the temperature of the water must remain
unchanged, till the caloric of fluidity is all evolved.
3. The evolution of caloric, during the congelation of
water, is well illustrated by the following experiment of Dr,
Crawford : — Into a round tin vessel put a pound of powdered
ice ; surround this by a mixture of snow and salt in a larger
\ vessel ; and stir the ice in the inner one, till its temperature
i is reduced to -f 4° of Fahrenheit. To the ice thus cooled,
i add a pound of water at 32°. One 5th of this will be frozen ;
and the temperature of the ice will rise from 4° to 32°. In
this instance, the caloric, evolved by the congelation of one
5th of a pound of water, raises the temperature of a pound
of ice 28°.
4. If we dissolve sulphate of soda in water, in the propor¬
tion of one part to five, and surround the solution by a freez-
[ ing mixture, it cools gradually down to 31°. The salt, at
t this point, begins to be deposited, and stops the cooling en-
r tirely. This evolution of caloric, during the separation of
a salt, is exactly the reverse of what happens during its so¬
lution*.
* Blagden, Philosophical Transactions, lxxviii. 290.
96
OF HEAT OR CALORIC?.
CHAP. Ill*
5. To a saturated solution of sulphate of potash in water,
or of any salt that is insoluble in alcohol, add an equal mea¬
sure of alcohol. The alcohol, attracting the water more
strongly than the salt retains it, precipitates the salt, and
considerable heat is produced.
SECTION IV.
Caloric the Cause of Vapour ,
I. Every liquid , ivhen of the same degree of chemical purity 9
and under equal circumstances of atmospheric pressure , has one
peculiar point of temperature , at which it invariably boils
Thus, pure water always boils at 212°, alcohol at 176°, and
ether at 98°, Fahrenheit; and, when once brought to the
boiling point, no liquid can be made hotter, however long
the application of heat be continued. The boiling point of
water may be readily ascertained, by immersing a thermo¬
meter in waiter boiling, in a metallic vessel, over the fire. As
there is some danger in applying heat directly to a vessel con¬
taining either ether or alcohol, the ebullition of these fluids
may be shown, by immersing the vessel containing them in
water, the temperature of which may be gradually raised.
The appearance of boiling is owing to the formation of vapour
at the bottom of the vessel, and its escape through the heated
fluid above it. That the steam, which escapes, is actually
formed at the bottom, and not at the top of the water, may
be seen by boiling some water in a Florence flask, or other
transparent vessel, over an Argand’s lamp. The bubbles of
vapour will all ascend from the bottom of the vessel. A few
exceptions to the fixity of the boiling point of liquids, arising
chiefly from the material of which the containing vessel is
composed, have lately been stated by Gay Lussac *.
II. Steam has exactly the same temperature as boiling water.—
Let a tin vessel be provided, having two holes in its cover,
one of which is just large enough to admit the stem of a
- _ _ - . — -r - . . r _ — - , - -i - ~ -
* Ann de Chira. et Phys. vii. 307, or Journ. of Science, v. 361.
4
SECT. IV.
CALORIC THE CAUSE OF VAPOUR.
97
thermometer. Fill it partly with water, and let the bulb of
the thermometer be an inch or two above the surface of the
water, leaving the other aperture open for the escape of
vapour. When the water boils, the thermometer, surrounded
by steam, will rise to 212°, which is precisely the tempera-
ture of the water beneath : yet water, placed on a fire, con¬
tinues to receive heat, very abundantly, even when boiling
hot ; and as this heat is not appreciable by the thermometer,
it must exist in the steam, in a latent state.
Perfectly formed steam is entirely invisible. We may
satisfy ourselves of this by boiling strongly a small quantity
of water in a flask ; for complete transparency will exist in
the upper part of the vessel. It is only when it begins to be
condensed, that steam becomes visible. We have a proof
also of the same fact in the thick fogs which are produced by
a sudden transition from warm to cold weather ; the vapour,
which was imperceptible at the higher temperature, being
condensed and rendered visible by the lower.
III. The boiling point of the same fluid varies , under different
degrees of atmospheric pressure.— Thus water, which has been
removed from the fire, and has ceased to boil, has its ebullition
renewed when it is placed under a receiver, the air of which
is quickly exhausted by an air pump. Alcohol and ether,
confined under an exhausted receiver, boil violently at the
temperature of the atmosphere. In general, liquids boil in
vacuo9 with about 140° less of heat, than are required under
a mean pressure of the atmosphere*. Even the ordinary
variations in the weight of the air, as measured by the baro¬
meter, are sufficient to make a difference in the boiling point
of water of about 5° between the two extremes f. On ascend¬
ing considerable heights, as to the tops of mountains, the
boiling point of water gradually falls on the scale of the ther¬
mometer. Thus on the summit of Mont Blanc, water was
found by Saussure to boil at 187° Fahrenheit. On this fact
is founded the use of the thermometer in the measurement of
* Black’s Lectures, i. 151.
f Sir G. Shuckburgh, in Philosophical Transactions, Ixxix. 375, and
Gen. Roy in ditto, lxvii. 687.
VOL. I
H
OF HEAT OR CALORIC.
CHAP. III.
98
heights, which though originally suggested by Fahrenheit,
has only lately been made conveniently practicable, in con¬
sequence of the invention of a thermometer, adapted to the
purpose, by the Rev. Mr. Wollaston*. Without entering
into minute details, it would not be possible to give a clear
idea of the instrument. It may be sufficient to state that each
degree about the boiling point is made to occupy a space, that
admits of being distinctly divided into 1000 parts. And as
each degree of Fahrenheit is equivalent to 0*589 of an inch of
the barometer, which indicates an elevation of 530 feet, it
follows that one thousandth part of a degree will be equiva¬
lent to a difference in height of about six inches. In fact, the
height of a common table produces a manifest difference in
the boiling point of water, as ascertained by this sensible in¬
strument.
The influence of a diminished pressure in facilitating ebulli¬
tion may, also, be illustrated by the following very simple ex¬
periment : — Place, over a lamp, a Florence flask, about three
fourths filled with water; let it boil briskly during a few
minutes; and, immediately on removing it from the lamp,
cork it tightly, and suddenly invert it. The water will now
cease to boil ; but, on cooling the convex part of the flask by
a stream of cold water, the boiling will be renewed. Apply¬
ing boiling water from the spout of a tea-kettle to the same
part of the flask, the water will again cease to boil. This
renewal of the ebullition, by the application of cold (an ap¬
parent paradox), is owing to the formation of an imperfect
vacuum over the hot water, by the condensation of steam;
and the suspension of the boiling, on re-applying the heat, to
the renewed pressure on the surface of the hot water, occa¬
sioned by the formation of fresh steam.
From these facts, it may be inferred, that the particles of
caloric are mutually repulsive, and that they communicate
this repulsive tendency to other bodies in which caloric is
contained. This repulsive power tends to change solids into
fluids, and liquids into aeriform bodies, and is chiefly counter¬
acted by the pressure of the atmosphere.
* Phil. Trans. 1817, p. 184. The instrument is sold by Mr, Carey in the
Strand,
SECT. IV. CALORIC THE CAUSE OF VAPOUR. 99
Were this counteracting cause removed, many bodies,
which at present have a liquid form, would cease to be such,
and would be changed into a gaseous state. Precisely the
same effect, therefore, results from the prevalence of either of
these forces. Add to certain liquids a quantity of caloric, in
other words, place them in a high temperature, and they are
immediately converted into gases : or, their temperature re¬
maining the same, diminish the weight of the atmosphere;
and the caloric, which they naturally contain, exerts its re¬
pulsive tendency with equal effect, and they are in like man¬
ner converted into gases. These facts are best shown by the
following experiments on ether :
1. Ether, at the temperature of 104°, exists in the state of
a gas. This may be shown by filling ajar with water of this
temperature, and inverting it in a vessel of the same. Then
introduce a little ether, by means of a small glass tube closed
at one end. The ether will rise to the top of the jar, and, in
its ascent, will be changed into gas, filling the whole jar with
a transparent, invisible, elastic fluid. On permitting the water
to cool, the ethereal gas is condensed, and the inverted jar
again becomes filled with water.
2. Ether is changed into gas by diminishing the weight of
the atmosphere. Into a glass tube, about six inches long, and
half an inch in diameter, put a tea-spoonful of ether, and fill
up the tube with water ; then, pressing the thumb on the open
end of the tube, place it, inverted, in a jar of water. Let the
whole be set under the receiver of an air pump, and the air
exhausted. The ether will be changed into gas, which will
expel the water entirely from the tube. On re- admitting the
air into the receiver, the gas is again condensed into a liquid
form.
IV. On the contrary , by considerably increasing the pressure ,
water may be heated to above 400° Fahrenheit , without being
changed into vapour. — This experiment requires, for its per¬
formance, a strong iron vessel, called a Papin’s digestor, a
plate of which may be seen in Gren’s Chemistry. That the
boiling point of water, and the temperature of steam, are raised
by an increased pressure, may be shown, however, by means
of the small boiler, represented plate v. fig. 46, which will be
100
OF HEAT OR CALORIC.
CHAP. IIJ*
found extremely useful in experiments on this subject. Its
precise size, and directions for its construction, will be given
in the Description of the Plates.
On the cock c may be screwed, occasionally, a valve, loaded
in the proportion of 14 pounds to the square inch. The boiler
being rather more than half filled with water, and the per¬
forated cap d being screwed into its place, the ball of the ther¬
mometer will be an inch or more above the surface of the
water, and will indicate its temperature, as well as that of the
steam, both being, necessarily, in all cases, precisely the same.
Allowing the steam to escape through the cock c, before affix¬
ing the valve, the temperature of the steam, under a mean atmos¬
pheric pressure, will be 212°. When an additional atmosphere
is added by the weighted valve, it will rise to above 240° ; by
a valve twice as heavy as the first, or loaded in the propor¬
tion of 42 pounds to the square inch ( = three atmospheres), the
temperature of the steam will be raised to nearly 270°. This
is as far as it is safe to carry the experiment ; but by substi¬
tuting a strong iron vessel, the numbers have been obtained,
which will be found in the form of a table, in the Appendix.
V. The absorption of caloric , during evaporation , shown by
experiment*— Moisten a thermometer with alcohol, or with
ether, and expose it to the air, repeating these operations
alternately. The mercury of the thermometer will sink at
each exposure, because the volatile liquor, during the evapora¬
tion, robs it of its heat. In this way (especially with the aid
of an apparatus described by Mr, Cavallo, in the Philosophi¬
cal Transactions, 1781, p. 509), water may be frozen in a
thin and small glass ball, by means of ether. The same effect
may be obtained, also, by immersing a tube, containing water
at the bottom, in a glass of ether, which is to be placed under
the receiver of an air pump ; or the ether may be allowed to
float on the surface of the water. During the exhaustion of
the vessel, the ether will evaporate rapidly ; and, robbing the
water of heat, will completely freeze it ; thus exhibiting the
singular spectacle of two fluids in contact with each other, one
of which is in the act of boiling, and the other of freezing, at
the same moment.
By a little modification of the experiment, mercury itself
SECT. IV.
CALORIC THE CAUSE OF VAPOUR.
101
which requires for congelation a temperature of almost 40®
below 0 of Fahrenheit, may be frozen, as was first shown by
Dr. Marcet*. A conical receiver, open at the top, is placed
on the plate of an air pump, and a mercurial thermometer is
suspended within the receiver, through the aperture, by means
of a brass plate, perforated in its centre, and fitting the re¬
ceiver air tight, when laid upon its open neck. The thermo¬
meter passes through this plate, to which it is fitted by a
leather adjustment, or simply by a cork secured with sealing
wax ; and it is so graduated, that, when its bulb is sunk a few
inches within the receiver, the stem rises externally through
the plate, above which the scale begins. The bulb is then
wrapped up in a little cotton wool, or, what is better, in a
small bag of fine fleecy hosiery ; and, after being dipped into
ether, the apparatus is quickly laid over the receiver, which
is exhausted as rapidly as possible. In two or three minutes
the temperature sinks to about 45° below 0, at which moment
the quicksilver in the stem suddenly descends with great rapi¬
dity. If it be desired to exhibit the mercury in a solid state,
common tubes may be used, which have originally been about
an inch diameter, but have been flattened by pressure, when
softened by the blow-pipe. The experiment succeeds, when
the temperature of the room is as high as 40° Fahrenheit.
VI. The fixation of caloric in water, by its conversion into
steam , may be shown by the following experiments 1. Let a
pound of water at 212°, and eight pounds of iron filings at
300°, be suddenly mixed together. A large quantity of vapour
will be instantly generated ; and the temperature of the mix¬
ture will be only 212°; but that of the vapour produced is
also not more than 212°; and the steam must therefore con¬
tain, in a latent or combined form, all the caloric which raised
the temperature of eight pounds of iron filings from 212° to
300°.
2. The quantity of caloric, which thus becomes latent
during the formation of steam, may be approximated, by re¬
peating the following experiment of Dr. Black : He placed
two cylindrical flat-bottomed vessels of tin, five inches in
* 34 Nich. Journal, 119.
102
OF HEAT OR CALORIC.
CHAP. III.
diameter, and containing a small quantity of water at 50°, on
a red hot iron plate, of the kind used in kitchens. In four
minutes the water began to boil, and in twenty minutes the
whole was boiled away. In four minutes, therefore, the water
received 162° of temperature, or 404-° in each minute. If we
suppose, therefore, that the heat continues to enter the water
at the same rate, during the whole ebullition, we must con¬
clude that 40-^° x 20 = 810° have entered the water, and are
contained in the vapour.
It has been found by experiment that 75 pounds of New¬
castle coal, or 100 pounds of coal of medium quality, applied
in the best manner, are required for the vaporization of 12
cubic feet, or about 89f wine gallons, of w ater. A pound of
coal, on the average, may be considered as equivalent to con¬
vert a gallon of water into vapour. Wood charcoal, by com¬
bustion, is capable of melting 94 times its weight of ice, and
of evaporating 13 times its weight of water, previously at 32°
Fahrenheit. Peat of the best quality, when properly applied,
evaporates 10 times its weight of water, but, as commonly
used, only 4 or 5 times. Even with the assistance of heated
air, only six times its weight can be evaporated, though
Curaudau pretends to have evaporated 25 times its weight*.
From evidence given before the House of Commons on the
Gas Light Bill, 174- pounds of good London coke appear to
be capable of raising from 66 to 70 pounds of water into
vapour, or about 4 times their weight f .
VII. Water , by conversion into steam , has its bulk prodigi¬
ously enlarged , viz, according to Mr. Watt's experiments , about
1800 times , or, according to Gay Lussac , ojdy 1698 times.— A.
cubic inch of water (or 252 grains) occupies, therefore, when
converted into steam, the space of about a cubic foot. Hence
its specific gravity, under the ordinary pressure of the air, is
to that of common air, nearly as 450 to 1 000 ; or, taking
Gay L ussac’s data, as 10 to 16, or 625 to 1000.
VIII. On the contrary , vapours , during their conversion into
a liquid form , evolve , or give out , much caloric. — The heat given
, - , _ _ — . — - - — — ■— i . ■■ — .... . . — .... . , ■ i .
* 79 An. Ch. 86.
f See also Count Rumford’s Researches on the Heat developed in Com¬
bustion. Phil. Mag. xli. xlii. and xliii.
SECT. IV. CALORIC THE CAUSE OF VAPOUR. 103
out, by the condensation of steam, is rendered apparent by
the following experiment : Mix 100 gallons of water at 50°,
with 1 gallon of water at 212°. The temperature of the water
will be raised about l-~°. Condense by a common still- tub,
1 gallon of water, from the state of steam, by 100 gallons of
water, at the temperature of 50°. The water will be raised
11°. Hence, 1 gallon of water, condensed from steam, raises
the temperature of 100 gallons of cold water 9-4° more than
1 gallon of boiling water; and, by an easy calculation, it
appears that the caloric imparted to the 100 gallons of cold
water by 8 pounds of steam, if it could be condensed in 1 gal¬
lon of water, would raise it to 950° *. The quantity of ice,
which is melted by steam of ordinary density, is invariably 74-
times the weight of the steam.
For exhibiting the latent heat of steam, by means of a small
apparatus, which may be placed on a table, and with the
assistance only of a lamp, the boiler already described (fig. 46)
will be found extremely well adapted. The right angled pipe
e must be screwed, however, into its place, and must be made
to terminate at the bottom of a jar, containing a known quan¬
tity of water of a given temperature. This conducting pipe
and the jar should be wrapped round with a few folds of
flannel. The apparatus being thus disposed, let the water in
the boiler be heated by an Argand’s lamp, with double con¬
centric wicks, till steam issues in considerable quantity through
the cock c, which is then to be closed. The steam will now
pass through the right angled pipe into the water contained
in the jar, which will condense the steam, and will have its
temperature very considerably raised. Ascertain the augmen¬
tation of temperature and weight; and the result will show,
how much a given weight of water has had its temperature
raised by a certain weight of condensed steam. To another
quantity of water, equal in weight and temperature to that
contained in the jar at the outset of the experiment, add a
quantity of water at 212°, equal in weight to the condensed
steam ; it will be found, on comparison of the two resulting
temperatures, that a given weight of steam has produced, by
* Black's Lectures, i. 169.
104
OF HEAT OR CALORIC.
CHAP. III.
its condensation, a much greater elevation of temperature,
than the same quantity of boiling water. This will be better
understood by the following example, taken from actual ex¬
periment :
Into eight ounces of water, at 50° Fahrenheit, contained
in the glass jar, fig. 46, steam was passed from the boiler,
till the temperature of the water in the jar rose to 173°. On
weighing the water, it was found to have gained 8L drachms;
that is, precisely 8-f drachms of steam had been condensed,
and had imparted its heat to the water. — To facilitate the ex¬
planation of this experiment, it is necessary to premise the
following remarks.
To measure the whole quantities of caloric contained in dif¬
ferent bodies, is a problem in chemistry which has not yet
been solved. But the quantities of caloric, added to, or sub¬
tracted from, different bodies (setting out from a given tem¬
perature) may, in many cases, be measured and compared
with considerable accuracy. Thus, if, as has been already
stated, two pounds of water at 120° be mixed with two pounds
at 60°, half the excess of caloric in the hot water will pass to
the colder portion ; that is, the hot water will be cooled 30°,
and the cold will receive 30° of temperature ; and if the ex¬
periment be conducted with proper precautions, 90°, the
arithmetical mean of the temperature of the separate parts,
will be the temperature of the mixture. If three pounds of
water at 100° be mixed with one pound at 60°, we shall have
the same quantity of heat as before, viz. four pounds at 90°.
Hence, if the quantity of water be multiplied by the tempe¬
rature, the product will be a comparative measure of the
quantity of caloric which the water contains, exceeding the
zero of the thermometer employed.
Thus, in the last example,
3 X 100 — 300 = the caloric above zero in the first portion.
lx 6 0 = 60 = the caloric above zero in the second do.
The sum, 360 = the caloric above zero in the mixture.
Dividing 360 by 4, the whole quantity of water, we obtain
90°, the temperature of the mixture.
SECT. IV.
CALORIC THE CAUSE OF VAPOUR.
105
This method of computation may be conveniently applied
to a variety of cases. Thus, in the foregoing experiment, 8-4
drachms of steam at 212°, added to 64 drachms of water at
50°, produced 7 2A drachms of water at 173°. Now,
724: x 173
64 x 50
= 12542^ = whole heat of the mixture.
C heat of 64 drachms, one of the
( component parts.
C heat of 8J- drachms, the other
(_ component part.
3200 =
9342-1
Therefore 9342-1 divided by 8-1 = 1099, should have been
the temperature of the latter portion {viz, 8-1 drachms), had
none of its heat been latent: and 1099 — 212 = 887 gives
the latent heat of the steam. This result does not differ more
than might be expected, owing to the unavoidable inaccuracies
of the experiment, from Mr. Watt’s determination, wrhich
states the latent heat of steam at 900°, or from that to 950° *.
Lavoisier, with the aid of the calorimeter, makes it 1000°, or
a little moref.
IX. The same weight of steam contains , whatever may he its
density , the same quantity of caloric; its latent heat being in¬
creased in exact proportion as its sensible heat is diminished ; and
the reverse . — This principle, though scarcely admitting of
illustration by any easy experiment, is one of considerable
importance ; and an ignorance of it has been the occasion of
many fruitless attempts to improve the economy of fuel in the
steam engine. The fact, so far as respects steam of lower
density than that of 30 inches of mercury, was long ago de¬
termined experimentally by Mr. Watt f. As the boiling
point of liquids is known to be considerably reduced under a
diminished pressure, it seemed reasonable to suspect that,
under these circumstances, steam might be obtained from them
with a less expenditure of heat. Water, Mr. Watt found,
might easily be distilled in vacuo when at the temperature of
only 70° Fahrenheit. But, by condensing steam formed at
this temperature, and observing the quantity of heat which it
communicated to a given weight of water, he determined that
* Black’s Lectures, i. 174. f Ibid. 175.
X Ibid. i. 190.
106
OF HEAT OR CALORIC.
CHAP. III.
its latent heat, instead of being only 955°, was between 1200°
and 1300°.
The same principle may be explained also by the following
illustration, which was suggested to me by Mr. Ewart. Let
us suppose that in a cylinder, furnished with a piston, we
have a certain quantity of steam, and that it is suddenly com¬
pressed, by a stroke of the piston, into half its bulk. None
of the steam will in this case be condensed ; but it will acquire
double elasticity, and its temperature will be considerably in¬
creased. Now if we either suppose the cylinder incapable of
transmitting heat, or take the moment instantly following the
compression before any heat has had time to escape, it must
be evident that the sensible and latent heat of the steam, taken
together before compression, are precisely equal to the sen¬
sible and latent heat taken together of the denser steam. But
in the dense steam, the sensible heat is increased, and the
latent heat proportionally diminished. The explanation of
this fact will be furnished by a principle to be hereafter ex¬
plained, that the capacities of elastic fluids for caloric are uni¬
formly diminished by increasing their density.
X. The evaporation of ruater is carried on much more rapidly
under a diminished pressure , especially if the vapour , which is
formed , be condensed as soon as it is produced , so as to keep up
the vacuum .
On this principle depends Mr. Leslie’s new and ingenious
mode of freezing water, in an atmosphere of medium tempe¬
rature, by producing a rapid evaporation from the surface of
the water itself. The water to be congealed is contained in a
shallow vessel, which is supported above another vessel, con¬
taining a strong sulphuric acid, or dry muriate of lime ; or
even dried garden mould or parched oatmeal. Any substance,
indeed, that powerfully attracts moisture, may be applied to
this purpose. The whole is covered by the receiver of an air
pump, which is rapidly exhausted ; and as soon as this is
effected, crystals of ice begin to shoot in the water, and a
considerable quantity of air makes its escape, after which the
whole of the water becomes solid. The rarefaction required
is to about 100 times; but to support congelation, after it has
2
SECT. IV. CALORIC THE CAUSE OF VAPOUR. 107
taken place, 20 or even 10 times are sufficient. The sulphuric
acid becomes very warm ; and it is remarkable, that if the
vacuum be kept up, the ice itself evaporates. In five or six
days, ice of an inch in thickness will entirely disappear. The
acid continues to act, till it has absorbed an equal volume of
water.
An elegant manner of making the experiment is to cover
the vessel of water with a plate of metal or glass, fixed to the
end of a sliding wire, which must pass through the neck of
the receiver, and be, at the same time, air tight, and capable
of being drawn upwards. When the receiver is exhausted,
the water will continue fluid, till the cover is removed, when,
in less than five minutes, needle-shaped crystals of ice will
shoot through it, and the whole will soon become frozen.
In this interesting process, if it were not for the sulphuric
acid, an atmosphere of aqueous vapour would fill the receiver;
and, pressing on the surface of the water, would prevent the
further production of vapour. But the steam, which rises,
being condensed the moment it is formed, the evaporation
goes on very rapidly, and has no limits but the quantity of
the water, and the diminished concentration of the acid *.
It is on the same principle, that the instrument invented by
Dr. Wollaston, and termed by him the Cryophorus, or Frost-
bearer , is founded. It may be formed by taking a glass tube,
having an internal diameter of about ~th of an inch diameter,
the tube being bent to a right angle at the distance of half
an inch from each ball, thus :
One of these balls should be about half filled with water, and
the other should be as perfect a vacuum as can readily be ob¬
tained, the mode of effecting which is well known to those
accustomed to blow glass. One of the balls is made to ter-
* The most complete account of this new mode of freezing is to be found
in the Supplement, now publishing, to the Encycl. Brit. art. Cold.
108
OF HEAT OR CALORIC.
CHAP. III.
minate in a capillary tube ; and when the water in the other
ball has been boiled over a lamp a considerable time, till all
the air is expelled, the capillary extremity, through which the
steam is still issuing with violence, is held in the flame of the
lamp, till the force of the vapour is so far reduced, that the
heat of the flame has power to seal it hermetically.
When an instrument of this kind is well prepared, if the
empty ball be immersed in a mixture of snow and salt, the
water in the other ball, though at the distance of two or three
feet, will be frozen solid in the course of a very few minutes.
The vapour in the empty ball is condensed by the common
operation of cold ; and the vacuum produced by this conden¬
sation gives opportunity for a fresh quantity to arise from the
opposite ball, with a proportional reduction of its temperature.
The large quantity of caloric, latent in steam, renders its
application extremely useful for practical purposes. Thus,
water may be heated, at a considerable distance from the
source of heat, by lengthening the conducting pipe e, fig. 46.
This furnishes us with a commodious method of warming the
water of baths, which, in certain cases of disease, it is of im¬
portance to have near the patient’s bed-room ; for the boiler,
in which the water is heated, may thus be placed on the
ground-floor, or in the cellar of a house ; and the steam con¬
veyed by pipes into an upper apartment. Steam may also be
applied to the purpose of heating or evaporating water, by a
modification of the apparatus. Fig. 46, g9 represents the ap¬
paratus for boiling water by the condensation of steam, with¬
out adding to its quantity ; a circumstance occasionally of con¬
siderable importance. The steam is received between the
vessel, which contains the water to be heated, and an exterior
case ; it imparts its caloric to the water, through the substance
of the vessel ; is thus condensed, and returns to the boiler by
the perpendicular pipe. An alteration of the form of the
vessel adapts it to evaporation (fig. 46, h ). This method of
evaporation is admirably suited to the concentration of liquids,
that are decomposed, or injured, by a higher temperature
than that of boiling water, such as medicinal extracts; to the
drying of precipitates, &c. In the employment of either of
SECT. V.
SPECIFIC CALORIC.
109
these vessels, it is expedient to surround it with some slow
conductor of heat. On a small scale, a few folds of woollen
cloth are sufficient ; and, when the vessel is constructed of a
large size for practical use, this purpose is served by the
brick-work in which it is placed.
SECTION V.
Specific Caloric .
Equal weights of the same body, at the same temperature,
contain the same quantities of caloric. But equal weights of
different bodies, at the same temperature, contain unequal
quantities of caloric. The quantity of caloric, which one
body contains, compared with that contained in another, is
called its specific caloric; and the power or property, which
enable bodies to retain different quantities of caloric, has been
called capacity for caloric. The method of determining the
specific caloric, or comparative quantities of caloric in different
bodies, is as follows :
It has already been observed, that equal weights of the
same body, at different temperatures, give, on admixture, the
arithmetical mean. Thus, the temperature of a pint of hot
water and a pint of cold, is, after mixture, very nearly half
way between that of the two extremes. But this is not the
case, when equal quantities of different bodies, at different tern*
peratures, are employed.
(a) If a pint of quicksilver at 100° Fahrenheit, be mixed
with a pint of water at 40°, the resulting temperature will not
be 70° (the arithmetical mean), but only 60°. Here the quick¬
silver loses 40° of heat, which nevertheless raise the tempera¬
ture of the water only 20° ; in other words, a larger quantity
of caloric is required to raise the temperature of a pint of wa¬
ter, than that of a pint of mercury, through the same num¬
ber of degrees. Hence it is inferred, that water has a greater
capacity for caloric than is inherent in quicksilver.
( b ) The experiment may be reversed, by heating the water
to a greater degree than the quicksilver. If the water be at
110
OF HEAT OR CALORIC.
CHAP. III.
100°, and the mercury at 40°, the resulting temperature will
be nearly 80° ; because the pint of hot water contains more
caloric, than is necessary to raise the quicksilver to the arith¬
metical mean.
(c) Lastly, if we take two measures of quicksilver to one of
water, it is of no consequence which is the hotter ; for the re¬
sulting temperature is always the mean between the two ex¬
tremes; for example, 70°, if the extremes be 100° and 40°.
Here, it is manifest, that the same quantity of caloric, which
makes one measure of water warmer by 30°, is sufficient for
making two measures of quicksilver warmer by the same num¬
ber. Quicksilver has, therefore, a less capacity than water
for caloric, in the proportion, when equal measures are taken,
of one to two.
If, instead of equal bulks of quicksilver and water, we had
taken equal weights , the disparity between the specific caloric
of the mercury and water would have been still greater. Thus
a pound of water at 100°, mixed with a pound of mercury at
40°, gives a temperature of 974°5 or 274° above the arithmeti¬
cal mean. In this experiment, the water, being cooled from
100° to 974° has lost a quantity of caloric reducing its tempe¬
rature only 2a° ; but this caloric, communicated to the pound
of mercury, has produced, in its temperature, a rise of no less
than 574°* Therefore, a quantity of caloric, necessary to
raise the temperature of a pound of water 24°> is sufficient to
raise that of a pound of mercury 574° » or, by the rule of pro¬
portion, the caloric, which raises the temperature of a pound
of water 1°, will raise that of a pound of quicksilver about
23°. Hence it is inferred, that the quantity of caloric con¬
tained in water, is to that contained in the same weight of
quicksilver as 23° to 1°. Or, stating the caloric of water at
1°, that of quicksilver will be Ag- part of 1°, or 0,0435 *.
When this comparison is extended to a great variety of bo¬
dies, they will be found to differ very considerably in their ca¬
pacities for caloric. The results of numerous experiments of
this kind are comprised in a table of specific caloric f.
* The above numbers, which differ from those commonly stated, are given
on the authority of Mr. Dalton.
f See the Appendix.
SECT. V.
SPECIFIC CALORIC.
in
The capacities of bodies for caloric influence, considerably,
the rate at which they are heated and cooled. In general,
those bodies are most slowly heated, and cool most slowly,
which have the greatest capacities for heat *. Thus, if water
and quicksilver be set, in similar quantities, and at equal dis¬
tances before the fire, the quicksilver will be much more ra¬
pidly heated than the water ; and, on removal from the fire, it
will cool with proportionally greater quickness than the water.
By ascertaining the comparative rates of cooling, we may even
determine, with tolerable exactness, the specific caloric of
bodies ; and particularly of one class (the gases), which are
not easily compared in any other way f. The specific heat of
the different aeriform fluids will be stated, on the authority of
Delaroche and Berard, in the chapter on gases.
* See Mattine, on Heat, page 74.
f See Leslie on Heat, chap. xxi. and Despretz Ann, de China, et Phys.
»i. 184,
112
t
CHAPTER IV
OF LIGHT.
The laws of light, so far as they relate to the phenomena of
its movement, and to the sense of vision, constitute the science
of optics; and are the objects, therefore, not of Chemistry,
but of Natural Philosophy. Light, however, is capable of
producing important chemical effects, and of entering into
various chemical combinations. Its action is, for the most
part, exerted in de-oxidizing bodies ; and facts of this kind
cannot be perfectly understood, until two important classes of
bodies have been described, viz. those of oxides and of acids.
In this place, therefore, I shall state only a few of its least
complicated effects ; and shall trace its agency on different bo¬
dies, as they become the objects of experiment in the sequel.
I. Light, in the state in which it reaches the organ of vision,
it is well known, is not a simple body, but is capable of being
divided, by the prism, into seven primary rays or colours,
viz . red, orange, yellow, green, blue, indigo, and violet. These
are refrangible in the above order, the red being least refran¬
gible, and the violet most so. The image formed by the dif¬
ferent rays, thus separated, constitutes the solar spectrum.
If it be divided into 300 parts, the red will occupy 45 of these
parts, the orange 27, the yellow 48, the green GO, the indigo
40, and the violet 80.
II. Heat and light are not present, in corresponding de¬
grees, in different parts of the solar spectrum. With respect
to the illuminating power of each colour, Dr. Herschell found
that the red rays are far from having it in an eminent degree.
The orange possess more of it than the red ; and the yellow
rays illuminate objects still more perfectly. The maximum of
illumination lies in the brightest yellow or palest green. The
green itself is nearly equally bright with the yellow; but from
the full deep green, the illuminating power decreases very
sensibly. That of the blue is nearly an a par with that of the
5
! CHAP. IV.
LIGHT.
113
red ; the indigo has much less than the blue, and the violet' is
very deficient *.
III. The heating power of the rays follow a different order.
— If the bulb of a very sensible air thermometer be moved in
succession, through the differently coloured rays, it will be
found to indicate the greatest heat in the red rays ; next in
the green ; and so on, in a diminishing progression, to the
violet. The precise effects of the different rays, determined
I by Dr. Herschell’s experiments, are as follows :
In the blue,
• - green,
- - yellow,
— — - full red,
r
The thermometer rose
_ _ A _
in 3 minutes from 55° to 56°
in 3 — 54 to 58
in 3 — 56 to 62
in 2\ — — — 56 to 72
confines of red, in 24. — — — 58 to 734
IV. When the thermometer is removed entirely out of the
confines of the red rays, but with its ball still in the line of the
spectrum, it rises even higher than in the red rays ; and con-
I tinues to rise, till removed half an inch beyond the extremity
i of the red rays. In this situation, quite out of the visible
i light, the thermometer rose in 2-L minutes from 61 to 79. The
i ball of the thermometer, employed for this purpose, should
be extremely small f, and should be blackened with Indian
i ink. An air thermometer is better adapted than a mercurial
one, to exhibit the minute change of temperature that ensues.
These invisible heat-making rays may be reflected by the
mirror, and refracted by the lens, exactly in the same manner
as the rays of light.
A fact has been ascertained by Dr. Delaroche, which seems
to point out a close connection between heat and light, and a
gradual passage of the one into the other. The rays of invi¬
sible heat pass through glass with difficulty, at a temperature
below that of boiling water ; but they traverse it with a facility
* Philosophical Transactions, 1800, page 267.
f Excellent thermometers for this purpose, and others requiring great
sensibility, are made by Mr. Crichton, of Glasgow, and Mr. Carey, of London,
VOL. I.
%
I
1 H
LIGHT.
CHAP. IV.
always increasing with the temperature, as it approaches the
point when bodies become luminous. From these experiments,,
it would appear that the modification, whatever it be, which
must be impressed on the invisible rays, to render them capa¬
ble of penetrating through glass, makes them approach more
and more to the state in which they must be, when they enter
the eye, and occasion the sensation of vision.
The experiments of Dr. Herschell, already confirmed by
Sir H. Englefield and other philosophers, were found correct
in the main, when repeated by Mr. Berard *, the same pro¬
gressive heating power being observed in the rays from the
violet to the red. But he found the greatest heating power
at the extremity of the spectrum, and not beyond it. He
fixed it at the point, where the bulb of the thermometer was
still entirely covered by the red ray ; and the thermometer
sunk progressively, in proportion as the distance of its bulb
from the red ray increased. Entirely out of the visible spec¬
trum, where Herschell fixed the maximum of heat, its eleva¬
tion above the ambient air was only one fifth of what it had been
«/
in the red ray itself. The reflection of invisible radiant heat,
Mr. Berard found, follows precisely the same law as that of
light.
V. Beyond the confines of the spectrum on the other side,
viz . a little beyond the violet ray, the thermometer is not af¬
fected; but in this place it is remarkable, that there are also
invisible rays of a different kind, which exert all the chemical
effects of the rays of light, and with even greater energy.
One of the chemical properties of light, it will hereafter be
stated, is, that it speedily changes, from white to black, the
fresh-precipitated muriate of silver f. This effect is produced
most rapidly by the direct light of the sun ; and the rays, as
separated by the prism, have this property in various degrees.
The blue rays, for example, effect a change of the muriate of
silver in 15 seconds, which the red require 20 minutes to ac¬
complish ; and, generally speaking, the power diminishes as
we recede from the violet extremity. But entirely out of the
spectrum, and beyond the violet rays, the effect is still pro-
* Thomsons Annals, ii. 163.
f See chap xviii. sect, iv.
CHAP* I V*
LIGHT.
IIS
duced. Hence it appears, that the solar beams consist of
three distinct kinds of rays : of those that excite heat, and
promote oxidation ; of illuminating rays ; and of de-oxidiz-
ing or hydrogenating rays. It has lately, also, been as¬
serted by Morrichini, that the violet rays have a magnetising
power, and are capable of reversing the poles of a needle al¬
ready magnetic *. A striking illustration of the different
power of the various kinds of rays is furnished, by their effect
on phosphorus. In the rays beyond the red extremity, phos¬
phorus is heated, smokes, and emits white fumes ; but these
are presently suppressed, on exposing it to the de-oxidizing
rays, which lie beyond the violet extremity.
“ I found,” says Sir H. Davy “ that a mixture of chlorine
and hydrogen acted more rapidly upon each other, combin¬
ing without explosion, when exposed to the red rays, than
when placed in the violet rays ; but that solution of chlorine
in water became solution of muriatic acid most rapidly, when
placed in the most refrangible rays of the spectrum. Puce-
coloured oxide of lead, when moistened, gradually gained a
tint of red in the least refrangible rays, and at last became
black, but was not affected in the most refrangible rays ; and
the same change was produced by exposing it to a current of
hydrogen gas. The oxide of mercury, procured by a solu¬
tion of potash and calomel, exposed to the spectrum, was not
changed in the most refrangible rays, but became red in the
least refrangible ones, which must have depended on its ab¬
sorbing oxygen. The violet rays produced, upon moistened
red oxide of mercury, the same effects as hydrogen gas.”
The experiments of Berard f confirm those of Ritter and
Wollaston. To show the disproportion between the energies
of the different rays, he concentrated, by means of a lens, all
that part of the spectrum, which extends from the green to
the extreme violet ; and, by another lens, all that portion,
which extends from the green to the extremity of the red. In
the focus of this last, though intensely bright to the eyes, mu-
* Ann. de Chim. etPhys. iii. 323 ; Jour, of Science, v. 138 ; and Thom¬
son's Annals, xii. 1.
f El. of Chem. Phil. p. 211. t Thomson’s Annals, ii. 165.
i 2
116
LIGHT.
CHAP. IV. ,
riate of silver remained above two hours unaltered ; but in i
that of the former, though much less bright, it was blackened t
in less than six minutes.
VI. There is an exception however; as stated by Dr. Wol¬
laston, to the de-oxidizing power of the rays above-mentioned. .
The substance, termed gum-guaiacum, has the property, when i
exposed to the light, of being changed from a yellowish co- *
lour to green ; and this effect he has ascertained to be con- •
nected with the absorption of oxygen. Now in the most re- *
frangible rays, which would fall beyond the violet extremity,
he found that this substance became green, and was again i
changed to yellow by the least refrangible. This is precisely
the reverse of what happens to muriate of silver, which is;
blackened, or de-oxidized, by the most refrangible ; and has »
its colour restored, or is again oxygenized, in the least re¬
frangible rays.
VII. Certain bodies have the property of absorbing the rays
of light in their totality ; of retaining them for some time ; ;
and of again evolving them unchanged, and unaccompanied I
by sensible heat. Thus, in an experiment of Du Fay, a dia- ■
mond exposed to the sun, and immediately covered witht
black wax, shone in the dark, on removing the wax, at the i
expiration of several months. Bodies, gifted with this pro- ■
perty, are called solar phosphori. Such are Canton’s,
Baldwin’s, Homberg’s, and the Bolognian phosphori, which t
will be described hereafter. To the same class belong: seve- •
ral natural bodies, which retain light, * and give it out un- ■
changed. Thus snow is a natural solar phosphorus. So also »
is, occasionally, the sea when agitated; putrid fish have ai
similar property; and the glow-worm belongs to the same?
class. These phenomena are independent of every thing like
combustion ; for artificial phosphori, after exposure to the sun’s
rays, shine in the dark, when placed in the vacuum of an air-
pump, or under water, &c., where no air is present to effect : !
combustion.
VIII. From solar phosphori, the extrication of light is
facilitated by the application of an elevated temperature ; and?
after having ceased to shine at the ordinary temperature, they
again emit light when exposed to an increase of heat. Several
CHAP. IV.
LIGHT.
117
bodies, which do not otherwise give out light, evolve it, or
become phosphorescent, when heated. Thus, powdered fiuate
of lime becomes luminous, when thrown on an iron plate
raised to a temperature rather above that of boiling water ;
and one of its varieties, known to mineralogists under the
name of chlorophane , gives out abundantly an emerald green
light by the mere heat of the hand ; and after being exposed
to the sun, or even to a candle, continues to shine in a dark
place for some time *. The yolk of an egg, when dried, be¬
comes luminous, on being heated; and so also does tallow
during liquefaction. To exhibit the last mentioned fact, it is
merely necessary to place a lump of tallow on a coal, heated
below ignition, making the experiment in a dark room.
IX. Attrition, also, evolves light. Thus, two pieces of
common bonnet cane, rubbed strongly against each other in
the dark, emit a faint light. Two pieces of borax have the
same property much more remarkably.
X. Light is disengaged in various cases of chemical com¬
bination. Whenever combustion is a part of the phenomena,
I this is well known to happen ; but light is evolved, also, in
other instances, where nothing like combustion goes forward.
Thus, fresh prepared pure magnesia, added suddenly to highly
concentrated sulphuric acid, exhibits a red heat.
XI. For measuring the relative intensities of light from
various sources, an instrument has been contrived, called the
photometer. That of Count Rumford, described in the
84th volume of the Philosophical Transactions, being founded
on optical principles, does not fall strictly within the province
of this work. It is constructed on the principle, that the
power of a burning body, to illuminate any defined space, is
directly as the intensity of the light, and inversely as the
square of the distance. If two unequal lights shine on the
same surface at equal obliquities, and an opaque body be inter¬
posed between each of them and the illuminated surface, the
two shadows must differ in intensity or blackness ; for the
shadow formed by intercepting the greater light will be illu¬
minated by the lesser light only ; and, reversely, the other
* Thomson’s Annals, ix. 17.
118
LIGHT.
CHAP. IV.
shadow will be illuminated by the greater light ; that is, the
stronger light will be attended with the deeper shadow. But
it is easy, by removing the stronger light to a greater distance,
to render the shadow, which it produces, not deeper than that
of the smaller, or of precisely the same intensity. This ;
equalization being effected, the quantity of light emitted by
each lamp, or candle, will be as the square of the distance of
the burning body from the white surface.
The photometer of Mr. Leslie is founded on a different
principle, viz. that light, in proportion to its absorption, pro¬
duces heat. The degree of heat produced, and consequently r I
of light absorbed, is measured by the expansion of a confined
portion of air. A minute description of the ingenious instru- • .
ment. contrived by Mr. Leslie with this view, may be seen iaui
his work on Heat, or in the 3d vol. of Nicholson’s 4to. Jour- ■ I
nal. In its construction, it bears a considerable resemblance* :
to the differential thermometer, already described, page 75,. .
and represented plate i. fig. 7. As both the balls of the latter f b
instrument, however, are transparent, no change ensues ini [I
the situation of the coloured liquid when it is exposed to the e rE
variations of light. But, in the photometer, one of the ballsslS
is rendered opaque, either by tinging the glass, or by coverings |
it with a pigment; and hence this ball, absorbing the incident! a
light which passes freely through the transparent one, the airr a
included in it becomes warmer than that of the other ball, |
and, by its great elasticity, forces the liquid up die opposite, i
leg of the instrument. A graduated scale measures the amount! i
of the effect; and a glass covering defends the photometer™*
from being influenced by the temperature of the atmosphere.
The important discoveries of Malus, respecting the polari- 1
sation of light, scarcely fall within the province of this work, 1
and I refer, therefore, for a popular statement of them to the r
33d vol. of Nicholson’s Journal, p. 344.
119
CHAPTER V.
OF GASES.
SECTION I.
Of the Apparatus for Gases.
I1 OR performing the necessary experiments on gases, many
articles of apparatus are essential, that have not hitherto been
described. It may assist the student in obtaining the neces-
sary instruments, if a few of the most essential be here enu¬
merated. In this place, however, I shall mention such only,
as are necessary in making a few general experiments on this
interesting class of bodies.
The apparatus, required for experiments on gases, consists
partly of vessels fitted for containing the materials that afford
them, and partly of vessels adapted for the reception of gases,
and for submitting them to experiment.
1. For procuring such gases as are producible without a
very strong heat, glass bottles, furnished with ground stop¬
pers and bent tubes, are sufficient (plate ii. fig. 18). Of these
several will be required, of different sizes and shapes, adapted
to different purposes. If these cannot be procured, a Florence
flask, with a cork perforated by a bent glass tube, or even by
a tin pipe, will serve for obtaining some of the gases.
Those gases that require, for their liberation, a red heat,
may be procured, by exposing to heat the substance capable
of affording them, in earthen retorts or tubes; or in a gun
barrel, the touch-hole of which has been accurately closed by
an iron pin. To the mouth of the barrel must be affixed a
glass tube, bent so as to convey the gases where it may be re¬
quisite.
A very convenient apparatus, for obtaining such gases as
cannot be disengaged without a red beat, is sold at the shops
120
GASES.
CHAP. V.
for philosophical apparatus in London. It consists of a cast-
iron retort, having a jointed metallic conducting tube fitted
to it by grinding ; by means of which the gas may be con¬
veyed in any direction, and to any moderate distance. It is
represented as placed, when in actual use, between the bars of
a common fire-grate (plate ix. fig. 85, a , b).
2. For receiving the gases, glass jars, of various sizes (figs.
21, 22, 23), are required, some of which should be furnished
with necks at the top, fitted with ground stoppers. Others
should be provided with brass caps, and screws, for the re¬
ception of air-cocks (fig. 22). Of these last (the air-cocks),
several will be found necessary ; and, to some of them, blad¬
ders, or elastic bottles, should be firmly tied, for the purpose
of transferring gases. These jars will also be found extremely
useful in experiments on the properties and effects of the gases.
Some of them should be graduated into cubical inches.
To contain these jars, when in use, a vessel will be ne¬
cessary, capable of holding a few gallons of water. This
may either be of wood, if of considerable size ; or, if small,
of tin, japanned or painted. Plate iv. fig. 41, ff exhibits a
section of this apparatus, which has been termed the pneu-
mato-chemical trough, or pneumatic cistern. Its size may
vary with that of the jars employed; and, about two or three
inches from the top, it should have a shelf, on which the jars
may be placed, when filled with air, without the risk of being
overset. In this shelf should be a few small holes, to which
inverted funnels may be soldered.
A glass tube, about 18 inches long, and three quarters of
an inch diameter (fig. 24), closed at one end, and divided into
cubic inches, and tenths of inches, will be required for ascer¬
taining the purity of air by nitrous gas. It should be accom¬
panied also with a small measure, containing about two cubic
inches, and similarly graduated. For employing the solution
of nitrous gas in liquid sulphate of iron, glass tubes, about
five inches long, and half an inch wide, divided decimally,
are also necessary. Besides these, the experimentalist .should
be furnished with air funnels (fig. 19), for transferring gases
from wide to narrow vessels.
An apparatus, almost indispensable in experiments on this
I SECT. I.
APPARATUS FOR GASES.
121
class of bodies, is a gazometer, which enables the chemist to
collect and to preserve large quantities of gas, with the aid
of only a few pounds of water. In the form of this apparatus
| there is considerable variety; but, at present, I have no other
i view than that of explaining its general construction and use.
| It consists of an outer fixed vessel d (plate iv. fig. 35), and an
inner moveable one c, both of japanned iron. The latter
i slides easily up and down within the other, and is suspended
by cords passing over pulleys, to which are attached the coun-
; terpoises, ee. To avoid the encumbrance of a great weight
; of water, the outer vessel d is made double, or is composed of
! two cylinders, the inner one of which is closed at the top and
at the bottom. The space of only about half an inch is left
between the two cylinders, as shown by the dotted lines. In
this space the vessel c may move freely up and down. The
interval is filled with water as high as the top of the inner
cylinder. The cup, or rim, at the top of the outer vessel, is
to prevent the water from overflowing, when the vessel c is
forcibly pressed down, in which situation it is placed whenever
gas is about to be collected. The gas enters from the vessel
in which it is produced, by the communicating pipe 5, and
passes along the perpendicular pipe marked by dotted lines in
the centre, into the cavity of the vessel c, which continues
rising till it is full.
To transfer the gas, or to apply it to any purpose, the
cock b is to be shut, and an empty bladder, or bottle of elastic
gum, furnished with a stop cock, to be screwed on a. When
the vessel c is pressed down with the hand, the gas passes
down the central pipe, which it had before ascended, and its
escape at b being prevented, it finds its way up a pipe which
is fixed to the outer surface of the vessel, and which is termi¬
nated by the cock a. By means of an ivory mouth-piece
screwed upon this cock, the gas, included in the instrument,
may be respired ; the nostrils being closed by the fingers.
When it is required to transfer thecas into glass jars standing
inverted in water, a crooked tube may be employed, one end
of which is screwed upon the cock b ; while the other aperture
is brought under the inverted funnel, fixed into the shelf of
the pneumatic trough. (See fig. 41, c.)
Several alterations have been made in the form of this ap-
122
GASES.
CHAP. V.
paratus ; but they are principally such as add merely to its
neatness and beauty, and not to its utility ; and they render
it less easy of explanation. The counterpoises ee are now,
generally, concealed in the framing, and the vessel c is fre¬
quently made of glass.
When large quantities of gas are required (as at a public lec¬
ture), the gas-holder (plate iv. fig. 36), will be found extremely
useful. It is made of tinned iron plate, japanned both within
and without. Two short pipes, a andc, terminated by cocks,
proceed from its sides, and another, b , passes through the
middle of the top or cover, to which it is soldered, and
reaches within half an inch of the bottom. It will be found
convenient also to have an air-cock, with a very wide bore,
fixed to the funnel at b. When gas is to be transferred into
this vessel from the gazometer, the vessel is first completely
filled with water through the funnel, the cock a being left
open, and c shut. By means of a horizontal pipe, the aper¬
ture a is connected with a of the gazometer. The cock b
being shut, a and c are opened, and the vessel c of the gazo¬
meter (fig. 35), gently pressed downwards with the hand.
The gas then descends from the gazometer till the air-holder
is full, which may be known by the water ceasing to escape,
through the cock c. All the cocks are then to be shut, and
the vessels disunited. To apply this gas to any purpose, an
empty bladder may be screwed on a ; and water being poured
through the funnel b , a corresponding quantity of gas is forced
into the bladder. By lengthening the pipe b , the pressure of
a column of water may be added : and the gas being forced
through a with considerable velocity, may be applied to the
purpose of a blow-pipe, &c. &c. The apparatus admits of
a variety of modifications. The most useful one appears to
me to be that contrived by Mr. Pepys, consisting chiefly in
the addition of a shallow cistern (e9 plate ix. fig. 85) to the
top of the air-holder, and of a glass register tube f9 which
shows the height of the water, and consequently the quantity
of iras, in the vessel. A more minute account of it will be
given in the description of the ninth plate *.
* Descriptions and figures of improved gas-holders may be seen also in
the 13th, 24th, 27th, and 44th vols. of the Philosophical Magazine.
SECT. I.
APPARATUS FOR GASES.
123
The gazometer, already described, is fitted only for the
reception of gases that are confineable by water ; because
quicksilver would act on the tinning and solder of the vessel,
and would not only be spoiled itself, but would destroy the
apparatus. Yet an instrument of this kind, in which mer¬
cury can be employed, is peculiarly desirable, on account of
the great weight of that fluid ; and two varieties of the mer-
i curial gazometer have therefore been invented. The one, of
; glass, is the contrivance of Mr. Ciayfieid, and may be seen
represented in the plate prefixed to Sir H. Davy’s Researches.
In the other, invented by Mr. Pepys, the cistern for the mer¬
cury is of cast-iron. A drawing and description of it may be
found in the 5th vol. of the Philosophical Magazine ; but as
neither of these instruments are essential to the chemical
student, and as they are required only in experiments of re¬
search, I deem it sufficient to refer to the minute descriptions
of their respective inventors. Mr. Newman has lately joined
a gazometer of this kind to an improved mercurial trough,
bv means of which the advantages of both are obtained with
only 60 or 70 pounds of quicksilver. A description and
drawing of this apparatus is given in the Journal of Science
and the Arts, i. 186.
For those gases that are absorbed by water, a mercurial
trough is necessary. For the mere exhibition of a few expe¬
riments on these condensible gases, a small wooden trough,
11 inches long, two wide, and two deep, cut out of a solid
block of mahogany, is sufficient; but for experiments of
research, one of considerable size is required. (See plate iii.
%• 31,//)
The apparatus, required for submitting gases to the action
of electricity , is shown in plate ix. fig. 84* ; where a represents
the knob of the prime conductor of an electrical machine;
b a Leyden jar, the ball of which is in contact with it, as
when in the act of charging ; and c the tube standing in¬
verted in mercury, and partly filled with gas. The mercury
is contained in a strong wooden box dy to which is screwed
the upright iron pillar e, with a sliding collar for securing the
tube c in a perpendicular position. When the jar b is charged
to a certain intensity, it discharges itself between the knob a
6
124
GASES.
CHAP. Ye
and the small ball i, which, with the wire connected with it,
may be occasionally fitted on the top of the tube c. The
strength of the shocks is regulated by the distance between
a and i.
By the same apparatus, inflammable mixtures of gases may
be exploded by electricity, In this case, however, the jar b
is unnecessary, a spark received by i from a being sufficient
to kindle the mixture.
The method of weighing gases is very simple, and easily
practised. For this purpose, however, it is necessary to be
provided with a good air-pump ; and with a globe or flask,
furnished with a brass cap and air-cock, as shown fig. 22, b.
A graduated receiver is also required, to which an air-cock is
adapted, as shown at fig. 22, a.
Supposing the receiver a to be filled with any gas, the
weight of which is to be ascertained, we screw the cock of
the vessel b on the transfer plate of an air-pump, and exhaust
it as completely as possible. The weight of the exhausted
vessel is then very accurately taken, even to a small fraction
of a grain ; and it is screwed upon the air-cock of the re¬
ceiver a. On opening both cocks, the last of which should
be turned very gradually, the gas ascends from the vessel a ;
and the quantity, which enters into the flask, is known by
the graduated scale on a. On weighing the vessel a second
time, we ascertain how many grains have been admitted. If
we have operated on common air, we shall find its weight to
be at the rate of about 30.5 grains to 100 cubical inches.
The same quantity of oxygen gas will weigh about 34 grains,
and of carbonic acid gas upwards of 47 grains.
In experiments of this kind it is necessary either to operate
with the barometer at 30 inches, and the thermometer at 60°
Fahrenheit, or to reduce the volume of gas employed to that
pressure and temperature, by rules which are given in the
Appendix. Great care is to be taken, also, not to warm any
of the vessels by contact with the hands, from which they
should be defended by a glove. On opening the communica¬
tion between the receiver and the exhausted globe, if any
water be lodged in the air-cock attached to the former, it will
be forcibly driven into the globe, and the experiment will be
SECT. I.
APPARATUS FOR GASES.
125
frustrated. This may be avoided by using great care in filling
the receiver with water, before passing into it the gas under
examination.
The specific gravity of any gas compared with common air
is readily known, when we have once determined its absolute
weight. Thus if 100 cubic inches of air weigh 30.5 grains,
and the same quantity of oxygen gas weighs 34 grains, we say,
30.5 : 34 : : 1.000 : 1.1147.
I The specific gravity of oxygen gas will therefore be as 1.1147
to 1.000. We may determine, also, the specific gravity of
; gases, more simply, by weighing the flask, first when full of
common air, and again when exhausted ; and afterwards by
admitting into it as much of the gas under examination as it
will receive ; and weighing it a third time. Now as the loss
between the first and second weighing is to the gain of weight
on admitting the gas, so is common air to the gas whose spe¬
cific gravity we are estimating. Supposing, for example,
that by exhausting the flask it loses 30.5 grains, and that by
admitting carbonic acid it gains 47 ; then
30.5 : 47 :: 1.000 1.5409.
The specific gravity of carbonic acid is therefore 1.5409, air
being taken at 1.000. And knowing its specific gravity, we
can, without any farther experiment, determine the weight
of 100 cubic inches of carbonic acid; for as the specific gra¬
vity of air is to that of carbonic acid, so is 30.5 to the num¬
ber required ; or
1.000 : 1.5409 :: 30.5 : 47.
One hundred inches of carbonic acid, therefore, will weigh
47 grains.
Previously to undertaking experiments on other gases, it
may be well for an unpractised experimentalist to accustom
himself to the dexterous management of gases, by transferring
common air from one vessel to others of different sizes.
1. When a glass jar, closed at one end, is filled with water,
and held with its mouth downwards, in however small a
quantity of wrater, the fluid is retained in its place by the
pressure of the atmosphere on the surface of the exterior water.
Fill in this manner, and invert, on the shelf of the pneumatic
trough, one of the jars, which is furnished with a stopper
126
GASES.
CHAP. V,
(fig. 23). The water will remain in the jar so long as the
stopper is closed ; but immediately on removing it, the water
will descend to the same level within as without ; for it is now
pressed, equally upwards and downwards, by the atmosphere,
and falls therefore in consequence of its own gravity.
2. Place the jar, filled with water and inverted, over one
of the funnels of the shelf of the pneumatic trough. Then
take another jar, filled (as it will be of course) with atmo¬
spherical air. Place the latter with its mouth on the surface
of the water : and on pressing it in the same position below
the surface, the included air will remain in its situation.
Bring the mouth of the jar beneath the funnel in the shelf,
and incline it gradually. The air will now rise in bubbles,
through the funnel, into the upper jar, and will expel the water
from it into the trough.
3. Let one of the jars, provided with a stop-cock at the
top be placed full of air on the shelf of the trough. Screw
upon it an empty bladder ; open the communication between
the jar and the bladder, and press the former into the -water.
The air will then pass into the bladder, till it is filled; and
when the bladder is removed from the jar, and a pipe screwed
upon it, the air may be again transferred into a jar inverted in
water.
4. For the purpose of transferring gases from a -wide vessel
standing over water, into a small tube filled with and inverted
over mercury, I have long used the following contrivance of
Mr. Cavendish. A tube, eight or ten inches long, and of
very small diameter, is drawn out to a fine bore, and bent at
this end, so as to resemble the italic letter /. The point is
then immersed in quicksilver, which is drawn into the tube
till it is filled, by the action of the mouth. Placing the finger
over the aperture at the straight end, the tube, filled with
quicksilver, is next conveyed through the water, with the
bent end uppermost, into an inverted jar of gas. When the
finger is removed, the quicksilver falls from the tube into the
trough, or into a cup placed to receive it, and the tube is filled
with the gas. The whole of the quicksilver, however, must
not be allowed to escape ; but a column must be left, three or
four inches long, and must be kept in its place by the finger.
SECT. I.
APPARATUS FOR GASES.
127
Remove the tube from the water ; let an assistant dry it with
blotting paper ; and introduce the point of the bent end- into
the aperture of the tube standing over quicksilver. On with¬
drawing the finger from that aperture which is now upper¬
most, the pressure of the column of quicksilver, added to the
weight of the atmosphere, will force the gas from the bent
rj tube into the one standing in the mercurial trough.
On every occasion, when it is necessary to observe the
precise quantity of gas, at the commencement and close of an
experiment, it is essential that the barometer and thermometer
; should exactly correspond at both periods. An increased
; temperature, or a fall of the barometer, augments the appa¬
ll rent quantity of gas ; and a reduced temperature or a higher
I barometer diminishes its bulk. Another circumstance, an
attention to which is indispensable in all accurate experiments,
i is that the surface of the fluid, by which the gas is confined,
should be precisely at the same level within and without the
jar. If the fluid be higher within the jar, the contained gas
will be under a less pressure than that of the atmosphere, the
weight of which is counterpoised by that of the column of
fluid within. In mercury, this source of error is of very con¬
siderable amount; as any person may be satisfied by pressing
down, into quicksilver, a tube partly filled with that fluid,
and partly with air, for the volume of the air will gradually
decrease, the deeper the tube is immersed.
In experiments on gases, it is not always possible, however,
to begin and conclude an experiment at precisely the same
temperature, or with the same height of the barometer; or
even to bring the mercury within and without the receiver to
the same level. In these cases, therefore, calculation becomes
necessary ; and with the view of comparing results more rea¬
dily and accurately, it is usual to reduce quantities of gas to
the bulk they would occupy under one given pressure, and at
a given temperature. In this country, it is now customary
to assume as a standard 30 inches of the barometer, and 60°
of Fahreheit’s thermometer ; and to bring to these standards
observations made under other degrees of atmospheric pres¬
sure and temperature. The rules for these corrections, which
are sufficiently simple, I shall give in the Appendix.
128
GASES*
CHAP. V.
Of experiments illustrative of the nature of gases in gene¬
ral, it may be proper to mention one or two that show the
mode in which caloric exists in this class of bodies. In vapours,
strictly so called, as the steam of water, caloric seems to be
retained with but little force ; for it quits the water when the
vapour is merely exposed to a lower temperature. But, in
gases, caloric is united by a very forcible affinity, and no
diminution of temperature, that has ever yet been effected,
can separate it from some of them. Thus the air of our at¬
mosphere, in the most intense artificial or natural cold, still
remains in the aeriform state. Hence is derived one character
of gases, viz. that they remain aeriform under almost all va¬
riations of pressure and temperature ; and in this class are
also included those aerial bodies, which, being condensed by
water, require confinement over mercury. The following ex¬
periment will show, that the caloric, contained in gases, is
chemically combined.
Into a small retort (plate ii. fig, 26, b) put an ounce or two
of well dried common salt, and about half its weight of sul¬
phuric acid. By this process, a great quantity of gas is pro¬
duced, which might be received and collected over mercury.
But, to serve the purpose of this experiment, let it pass
through a glass balloon, c, having three openings, into one of
which the neck of the retort passes, while, from the other, a
tube e proceeds, which ends in a vessel of water, of the
temperature of the atmosphere. Before closing the apparatus,
let a thermometer, d, be included in the balloon, to show the
temperature of the gas. It will be found that the mercury, in
this thermometer, will rise only a few degrees, whereas the
water, in the vessel which receives the bent tube, will soon
become boiling hot. In this instance, caloric flows from the
lamp to the muriatic acid, and converts it into gas ; but the heat,
thus expended, is not appreciable by the thermometer. The
caloric, however, is again evolved, when the gas is condensed
by water. In this experiment, we trace caloric into a latent
state, and again into the state of free or uncombined caloric.
A considerable part of the caloric, which exists in gases in
a latent state, may be rendered sensible by rapid mechanical
compression. Thus if air be suddenly compressed in the ball
SECT. I.
APPARATUS FOR GASES.
129
of an air-gun, the quantity of caloric liberated by the first
stroke of the piston, is sufficient to set fire to a piece of the
tinder called amadou #. A flash of light is said, also, to be
perceptible at the moment of condensation. This fact has
been applied to the construction of a portable instrument for
lighting a candle. It consists of a common syringe, concealed
in a walking stick. At the lower extremity, the syringe is
furnished writh a cap, which receives the substance intended to
be fired, and which is attached to the instrument by a male and
female screw. The rapid depression of the piston condenses
the air, and evolves sufficient heat to set the tinder on fire f.
For demonstrating the influence of variations of atmospheric
pressure on the formation of gases, better experiments cannot
be devised than those of Lavoisier But as some students,
who have the use of an air-pump, may not possess the appa¬
ratus described by Lavoisier (the glass bell and sliding wire), it
may be proper to point out an easier mode of showing the
same fact. This proof is furnished by the experiment already
described, in which ether is made to assume alternately an
aeriform and liquid state, by removing and restoring the pres¬
sure of the atmosphere.
Gases, when once formed, undergo a considerable change
of bulk by variations of external pressure. The general law9
which has been established on this subject is, that the volume
of gases is inversely as the compressing force. If, for example,
we have a quantity of gas occupying 60 cubic inches, under
the common pressure of the atmosphere, it will fill the space
of only 30 cubic inches, or one half, under a double pressure ;
of 20 inches, or one 3d, under a triple pressure; of 15
inches, or one 4th, under four times the pressure ; and so on.
When the pressure is sudden, considerable heat is evolved ;
and it appears, from Gay Lussac’s experiments, that different
gases, when equally compressed, give out different quantities
of heat, bearing probably a proportion to their specific heats.
The law of the dilatibility of gases by heat has already been
stated to be an enlargement of about ^-F-th part of their bulk
* Philosophical Magazine, xiv. 363, and xl. 424.
f Philosophical Magazine, xxxi. 130.
J See his Elements, chap. 1,
K
VOL. I.
130
GASES.
CHAP. V.
for each degree of Fahrenheit’s scale, between the freezing
and boiling points of water. At a temperature capable of
rendering glass luminous (probably about 1035° Fahrenheit),
1 volume becomes about 2.5
Before dismissing the consideration of the gases in general,
there are a few properties, which it may be proper to notice,
with the view of comparing the degree in which they belong
to different individuals of the class.
I. The exact specific gravity of the different gases is a most
important element, in calculating the proportion of the ingre¬
dients of compounds, into which they enter. Nothing, indeed,
can show the importance of this object more strikingly, than
the fact, that on the precise specific gravities of hydrogen
and oxygen gases, depend the whole series of numbers, which
are used to express the weights of the atoms of bodies on the
Daltonian theory. The following Table exhibits the specific
gravities of the most important of this class of bodies.
*
TABLE OF THE SPECIFIC GRAVITY OF GASES +.
Barometer 30. Thermometer 60°.
Names of Gases.
Specific
gravity.
Wt. of
100 cub.
inches.
Authority.
Atmospherical air .
1 .0000
Grains.
30.50
Shuckburgb.
* Oxygen gas . . .
1.1088
33.82
Allen and Pepys,
w ... 1
Ditto ........ . . .
1,10359
Biot and Arago.
Ditto.
CL SJ
g 3 s
Hydrogen gas . . . .
0.7321
2.23
m ^ 1
1 Nitrogen gas .
0.9691
29.55
Ditto.
^Chlorine gas .
2.5082
76.50
Davy.
<r>
rAmmoniacal gas .
0.5960
18.18
Allen and Pepys.
3
Carbd.Hy d r.from stagnant water
0.666
20.66
Dalton.
m
Olefiant gas . . .
0.974
29.72
Thomson.
S3
&
Pnosphureted hydrogen .
0.852
25.98
Dalton and Henry.
6 •
Ditto . . . . .
0.435
13.26
Davy.
« So -l Hydro-phosphoric Gas .
0.870
26.53
Ditto.
c ^
Sulphureted hydrogen .
1.177
35.89
Ditto.
P
O
Ditto .
1.231
38.17
Thenard.
ft
c
Arsenu reted hydrogen .
0.529
16.13
Tromsdorffo
a
o
Vapour of alcohol .
2.100
65.
Dalton.
O
Ditto of sulphuric ether .
2.250
70.
Ditto.
* Davy, Phil. Trans. 1817. p. 54.
f Gay Lussac’s Table, which is more copious, but in which the numbers
are not reduced to a mean of the barometer and thermometer, is copied into
Thomson’s Annals, ix. 16. ; a Table by Professor Meinecke of Halle is in¬
serted in the Journal of Science, &c. iii. 415.
SECT. I.
GENERAL PROPERTIES OF GASES®
131
Table of Specific Gases continued .
Names of Gases.
Specific
Gravity.
Wt. of
100 cub.
inches.
Authority.
r •
^Carbonic oxide ...............
0.96T
Grains.
30.19
Cruickshank*
Davy.
Ditto.
Be rard.
Nitrous oxide. ................
1.614
49.22
11
Nitrous gas . .
Di tto ........................ .
1.049
1.0388
32.
31.684
f Carbonic acid .................
1.518
46.31
Saussure.
Ditto. ........................
1.5495
47.26
Allen and Pepys.
Davy and Biot.
Davy.
Ditto.
VI
Muriatic acid.................
1.278
38.97
rr.
Nitric acid . . . ........ .... .. ...
2.425
76.
Sulphureous acid ..............
2.193
66.89
Di tto ........................ .
2.303
70.24
Gay Lussac.
John Davy,
Ditto.
<3
<
Phosgene gras. .... . ...........
3.3894
105.97
Silieated fluoric . . . .
2.990
91.19
72.31
^Fluoboracic ...................
2.370
Ditto.
II. The determination of the specific heat of gases is a diffi¬
cult and important problem, which has successively employed
the labour and ingenuity of Crawford, Lavoisier and De la
Place, Leslie, Gay Lussac, Dalton, and Delaroche and Be«
rard. The results of the two last-mentioned philosophers,
having been attained with the advantages of an improved state
of the science, and of instruments of the greatest delicacy and
refinement, are perhaps most entitled to confidence. The de¬
tails of their experiments are given in the S5tli volume of the
Annales de Chimie, preceded by an historical review of the
labours of their predecessors. The following Table contains
the general results.
TABLE OF THE SPECIFIC HEATS OF SOME GASES.
Names of Gases.
Under
equal
volumes.
Under
equal
weights.
Specific
gravities.
Atmospheric air . . . . . .
1.0000
1.0000
1 .0000
Hydrogen gas . . . . . . .
0.9033
12,340
0.0732
Oxygen gas . . . . .
0.9765
0,8848
1.1036
Nitrogen gas . . . . . . . .
1.0000
1,0318
0.9691
Nitrous oxide . .
1.3503
0,8878
1,5209
Olefiant gas . . .
1,5530
1.5763
0.9885
Carbonic oxide . . .
1.0340
1.0805
0.9569
Carbonic acid . .
1.2583
0.8280
1.5196
III. All solid bodies , that possess a certain degree of porosity,
are capable of absorbing gases. This was first observed in char¬
coal, the power of which to condense different gases will be
fully described in the section on that substance. It has been
K %
132
GASES*
CHAP. V.
found, also, by Saussure, jun. to belong to a stone called
meerschaum, to adhesive slate, asbestos, rock cork, and other
minerals ; and to raw silk and wool. The following general
principles are deducible from the experiments of Saussure *.
1. It is necessary to deprive the solid of the air which it
naturally contains. When of a nature not to be injured by
heat, this is most effectually done by igniting the solid, and
quenching it under mercury, where it is to be kept, till ad¬
mitted to a given volume of the gas to be absorbed. Solids
that are decomposable by heat may be deprived, though less
effectually, of air, by placing them under a receiver, which
must then be exhausted by the air-pump.
3. The same solid absorbs different quantities of different
gases. Charcoal for instance condenses 90 times its bulk of
ammoniacal gas, and not quite twice its bulk of hydrogen.
3. Solids, chemically the same, absorb different quantities
of the same gas, according to their state of mechanical aggre¬
gation. Thus the dense charcoal of box-wood absorbed 74-
volumes of air, while a light charcoal, prepared from cork,
did not absorb a sensible quantity.
4. Different solids absorb different quantities of the same
gas ; the quantity of carbonic acid absorbed by charcoal being
about seven times greater than that absorbed by meerschaum.
5. When the solid exerts no chemical action on the gas,
the absorption is terminated in 24 or 36 hours.
6. The effect of moistening the solid is to retard the absorp¬
tion and to diminish its amount; and when a gas has actually
been absorbed, it is again driven out unchanged, partly by
water of the ordinary temperature, and entirely by exposure
to a boiling heat.
7. During the absorption of a gas by a solid, the tempera¬
ture of the latter rises several degrees, and bears a proportion
to the absorbability of the gas, and the rapidity with w hich it
is condensed.
8. Solids condense a greater number of volumes of the more
absorbable gases under a rare than under a dense atmosphere;
but if the absorption be reckoned by weight, it is most consi¬
derable under the latter state.
* Thomson’s Annals, vi, 241.
SECT. I.
GENERAL PROPERTIES OF GASES.
133
9. When a solid saturated with any one gas is introduced
into an atmosphere of any other gas, a portion of the first is
expelled, and a part of the second takes its place.
IV. Gases are absorbed by liquids. On this subject the fol¬
lowing general principles may be laid down.
1. The same liquid absorbs different quantities of different
gases. Thus water takes up its own bulk of carbonic acid,
and not one fiftieth of its bulk of hydrogen gas.
2. Different liquids absorb different quantities of the same
gas. Alcohol, for instance, absorbs almost twice as much car¬
bonic acid, as is taken up by an equal volume of water.
3. The absorption is promoted by first freeing the liquid
from air, either by long continued boiling in a vessel with a
narrow neck, or by the air-pump. It requires, also, brisk
and long continued agitation, especially with the less absorb¬
able gases.
4. It does not appear that the gases are absorbed by all
liquids in the same order. For example, of four gases naphtha
absorbs most olefiant gas ; oil of lavender most nitrous oxide ;
olive oil most carbonic acid ; and solution of muriate of potash
most carbonic oxide.
5. The viscidity of liquids, though it does not much influ¬
ence the amount absorbed, occasions a longer time to be spent
in effecting the absorption. On the other hand, the amount
of any gas which is absorbed by water, is diminished by first
dissolving in the water any saline substance.
6. In general the lightest liquids possess the greatest power
of absorbing gases ; whereas, when there is no evident chemi¬
cal action, the heaviest gases are absorbed most copiously and
rapidly by the same liquid.
7. The temperature of a liquid is raised by the absorption
of a gas, in proportion to the amount and the rapidity of the
absorption.
8. In all liquids the quantities of gases absorbed are directly
as the pressure. For example, a liquid, which absorbs its
own bulk of gas under the pressure of the atmosphere, will
still absorb its own bulk of the same gas under double, triple,
&c. pressure ; but its own bulk of gas, twice compressed, is equal
to double its bulk of gas ordinarily compressed, and so on.
134
GASES.
CHAP. V.
9. When any liquid is agitated with a limited quantity of
any mixture of two gases, it does not absorb one only to the
exclusion of the other, but it absorbs Loth. In this case, the
quantities, which it takes up of each, are such, that the densi¬
ties of the gases are the same in and out of the liquid, after
the absorption is completed. Thus when 20 measures of pure
carbonic acid are agitated with 10 of common air, at least 10
measures of gas are absorbed. But from a mixture of 20
measures of carbonic acid with 10 of common air only fds
of 10 (= 6.6) are absorbed by 10 measures of water ; and the
gas, both in and out of the water, is two thirds carbonic acid
and one third air, at the close of the experiment.
The principle, on which gases are absorbed and retained by
liquids, is still a subject of controversy. By Berthollet, Thom¬
son, Saussure, and the generality of chemists, it is ascribed
to the exertion of a chemical affinity between the gas and the
liquid; but it is contended by Mr. Dalton and myself that
the effect in most cases is chiefly, if not wholly, mechanical.
The discussion would lead me into details of too great a
length ; anil I refer, therefore, for a statement of the argument,
to two papers which I have published in the 8th and 9th
volumes of Nicholson’s Journal; to Mr. Dalton’s New System
of Chemical Philosophy; and to his reply, in the 7th volume
of Dr. Thomson’s Annals, to the objections, which had been
advanced against the mechanical theory, by Saussure, in the
6th volume of the same work.
V. The velocities, with which different gases, when con¬
densed artificially by the same degree of pressure, escape
through a capillary tube, has been shown by Mr. Faraday to
vary very considerably The following table shows the com¬
parative times required by some of the gases to escape from a
vessel in which they were all equally compressed at the outset,
till their density arrived at an atmosphere and a quarter.
Carbonic acid required . 156.5 minutes.
Olefiant gas . . 135.5
Common air. . . 128
Coal gas . 100
Hyd rogen . . 57
* Journal of Science, &c. iii. 354.
SECT. II.
GENERAL PROPERTIES OF GASES.
135
These differences cease to exist at low pressures ; but under
the circumstances which have been stated, there seems reason
to believe that the velocities, with which gases escape through
capillary tubes, are inversely as their specific gravities, or in
some proportion approaching this.
VI. The colour of the electric spark, when transmitted through
different gases, has been observed by De Grotthus * to be as
follows :
In atmospheric air of double density, the spark was more
brilliant, but not coloured.
In hydrogen gas . . purple.
— phosphureted hydrogen ............ red.
— ammonia . . . red.
•— dry carbonic acid gas . . . violet
— - oxygen gas . . . ditto
— * aqueous vapour ................... orange.
vapour of ether i , j
.f _ . _ 7 l ................ . celadon green.
— ditto ox alcohol j
The general inference from his experiments is, that the
intensity of electric light is always in a direct proportion to
the density of the gas, and in the inverse proportion to the
conducting power of the gas for electricity.
VII. The comparative soniferous properties of the gases have
been determined by Messrs, Kerby and Merrick ; but as these
belong rather to mechanical than to chemical science, I shall
content myself with referring to the account of them in the
27th and 33d volumes of Nicholson’s Journal, and in the 45th
volume of the Philosophical Magazine.
SECTION XI.
Oxygen Gas »
We have no knowledge of the properties of oxygen in a
state of complete separation. In the most simple form, under
which we can procure it, it is combined with caloric, and pro¬
bably with light and electricity, constituting oxygen gas.
* 82 An. de Ch. 34.
136
GASES.
CHAP. V*
I. Oxygen gas may be procured from various substances.
1. From the black oxide of manganese, heated to redness
in a gun-barrel, or in an iron or earthen retort ; or, from the
same oxide, heated by a lamp in a retort or gas bottle, with
half its weight of strong sulphuric acid.
2. From the red oxide of lead (the common red lead used
by painters), heated either with or without sulphuric acid.
3. From various other oxides, as will be hereafter men¬
tioned.
4. From nitrate of potash (common saltpetre) made red-hot
in a gun-barrel, or in an earthen retort.
5. From oxy-muriate of potash, heated in a small glass
retort, over an Argand’s lamp. The oxygen gas thus pro¬
duced, is much purer than that obtained in any other mode,
especially the last portions, which should be kept separate.
All these substances, after having yielded oxygen gas, are
found considerably diminished in wreight; and calculating
each cubic inch of gas to be equal to one third of a grain, the
loss of weight will be found pretty exactly equivalent to that
of gas generated.
II. This gas has the following properties :
1. It is not absorbed by water*, or, at least, is so sparingly
absorbed, that, when agitated in contact with water, no per¬
ceptible diminution takes place.
2. It is rather heavier than common air. Sir H. Davy ori¬
ginally stated 100 cubic inches at 55° Fahrenheit, and 30
inches of the barometer, to weigh 35.06 grains ; and at the
temperature of 60°, the same quantity would weigh 34.70, or,
according to the same author, in his Elements of Chemical
Philosophy, 34 grains. Messrs. Allen and Pepys have de¬
termined 100 cubic inches to weigh 33.82 grains, the baro¬
meter being 30, and thermometer 60°. By Biot and Arago
its specific gravity is stated to be 1.10359.
* In this as in several other instances, where a gas is said not to be
absorbed by water, the assertion is not to be taken strictly, but merely as
implying that only a minute and difficultly appreciable portion is absorbed.
The precise proportion of each gas absorbed by water is stated in chap. vi.
sec. iii. in the form of a table.
SECT. IT.
OXYGEN GAS.
137
2. All combustible bodies burn in oxygen gas with greatly in¬
creased splendour.
( a ) A lighted wax taper, fixed to an iron wire, and plunged
into a vessel of this gas, burns with great brilliancy, pi. iv. fig.
38. If the taper be blown out, and let down into a vessel of
the gas while the snuff remains red-hot, it instantly rekindles,
with a slight explosion.
( b ) A red-hot bit of charcoal, fastened to a copper wire*
and immersed in the gas, throws out beautiful sparks.
(c) The light of phosphorus, burnt in this gas, is the
brightest that can be in any mode produced. Let the phos¬
phorus be placed in a small hemispherical tin cup, which may
be raised by means of the wire stand, pi. ii. fig. 25, two or
three inches above the surface of water contained in a broad
shallow dish. Fill a bell-shaped receiver, having an open
neck at the top, to which a compressed bladder is firmly tied,
■with oxygen gas ; and, as it stands inverted in water, press a
circular piece of pasteboard, rather exceeding the jar in dia-
; meter, over its mouth. When an assistant has set fire to the
phosphorus, cover it instantly with the jar of oxygen gas, re-
taming the pasteboard in its place, till the jar is immediately
< over the cup. When this has been skilfully managed, a very
j small portion only of the gas will escape ; and the inflamma-
: tion of the phosphorus will be extremely brilliant. The ex-
| panded gas rises into the flaccid bladder, and is thus prevented
i from escaping into the room, and proving disagreeable by its
suffocating smell.
(d) Substitute, for the phosphorus in experiment c, a small
! ball formed of turnings of zinc, in which about a grain of
phosphorus is to be inclosed. Set fire to the phosphorus, and
cover it expeditiously with the jar of oxygen. The zinc will be
i inflamed, and will burn with a beautiful white light. A similar
experiment may be made with metallic arsenic, which may be
n moistened with spirit of turpentine. The filings of various
i metals may also be inflamed, by placing them in a small cavity,
<i formed in a piece of charcoal, igniting the charcoal, and blow-
i ing, on the part containing the metal, a stream of oxygen gas.
(e) Procure some thin harpsichord wire, and twist it round
a slender rod of iron or glass, so as to coil it up in a spiral
138
GASES*
CHAP. V.
form. Then withdraw the rod, and tie a little thread or flax
round one end of the wire, for about one 20th of an inch ;
which end is to be dipped into melted sulphur. The other
end of the wire is to be fixed into a cork ; so that the spiral
may hang vertically (fig. 39). Fill, also, with oxygen gas, a
bottle capable of holding about a quart, and set it with its
mouth upwards. Then light the sulphur, and introduce the
wire into the bottle of gas, suspending it by the cork. The
iron will bum with a most brilliant light, throwing out a
number of sparks, which fall to the bottom of the bottle, and
generally break it. This accident, however, may frequently
be prevented by pouring sand into the bottle, so as to lie
about half an inch deep on the bottom (see pi. iv. fig. 39).
According to Mr. Accum *, a thick piece of iron or steel, such
as a file, if made sharp pointed, may be burnt in oxygen gas.
A small bit of wood is to be stuck upon its extremity, and set
on fire, previously to immersion in the gas.
(f) A little of Homberg’s pyrophorus, a substance to be
hereafter described, when poured into a bottle full of this gas,
immediately flashes like inflamed gunpowder.
From this detail of its properties, it appears, therefore, that
oxygen gas is eminently a supporter of combustion. It was
long, indeed, supposed to be the only supporter, and the pre¬
sence of oxygen was imagined to be essential to combustion.
It will appear, however, in the sequel that other simple bodies,
capable of existing in an aerial form, are equally entitled to
rank as supporters of combustion. Among these are chlorine,
iodine, and possibly fluorine. But they do not all support the
combustion of the same substances; charcoal, for example,
does not burn in chlorine, and potassium is the only body
that is known to burn in the vapour of iodine.
III. During every combustion in oxygen gas , the gas suffers
a considerable diminution. — To exhibit this, experimentally, in i
a manner perfectly free from all sources of error, would re- -
quire such an apparatus as few beside adepts in chemistry are
likely to possess. The apparatus required for this purpose is
described in the 6th chapter of Lavoisier’s Elements. The .»
t
»
* Nicholson’s Journal, 8vo. i. 320.
TTT
i*ECT II.
OXYGEN GAS.
139
fact may, however, be shown, less accurately, in the following
manner : Fill, with oxygen gas, a jar of moderate size, which
has a neck and ground-glass stopper at the top. Then, with
the assistance of a stand, formed of bent iron wire (pi. ii. fig.
25), place a shallow tin vessel, containing a bit of phosphorus
or sulphur, three or four inches above the level of the water
of a pneumatic trough. Invert the jar of oxygen gas, cauti¬
ously, and expeditiously, over this cup, so as to confine it, with
its contents, in the gas, and, pressing down the jar to the
bottom of the trough, open the stopper. A quantity of gas
will immediately rush out, and the water will rise to the same
level within the jar as without. When this has taken place,
set fire to the sulphur or phosphorus by a heated iron wire,
and instantly put in the stopper. The first effect of the com¬
bustion will be a depression of the water within the jar ; but
when the combustion has closed, and the vessel has cooled, a
considerable absorption will be found to have ensued.
Those persons who are possessed of a mercurial apparatus
may repeat this experiment in a less exceptionable manner.
On the surface of the quicksilver let a small hemispherical
cup float, made of untinned sheet-iron ; and, in order to keep
it from the sides of the jar, it may rest on a wire-stand,
shaped like the figure 43, plate iv. Let a jar, the height and
diameter of which must be regulated by the size of the mer¬
curial trough, be filled with oxygen gas over water, and be
removed, by means of a piece of pasteboard, as before de¬
scribed, to the mercurial bath, inverting it dexterously over
the tin cup. If the phosphorus had been previously set on
fire, a large quantity of the gas, expanded by the heat, would
have escaped, and would have prevented the accurate mea¬
surement of the absorption. After drying the surface of the
mercury within the jar by blotting paper, a portion of the
included gas must, therefore, be removed. This is done by
an inverted syphon, one leg of which is to be introduced (in
the same manner as is shown at fig. 41, g) within the jar be¬
fore placing it over the mercury ; and the gas will be forced
through the open extremity of the other, when the jar is
pressed down into the quicksilver. When the proper quail-
140
GASES.
CHAP. V.
tlty has been expelled, remove the syphon. The cup, con¬
taining the phosphorus, will thus rest on the surface of the
quicksilver within the jar, and above the level of the mercury
without. The phosphorus is to be inflamed by passing a
crooked iron wire, made red hot, through the quicksilver.
On the first impression of the heat arising from its combus¬
tion, the included gas will be considerably expanded ; but when
the phosphorus has ceased to burn, a considerable absorption
will be found to have taken place, the amount of which may
be measured by ascertaining the height of the quicksilver
within the jar, before and after the experiment. The quantity
of phosphorus employed should be very small, and should not
bear a greater proportion than that of 10 grains to each pint
of gas; otherwise the combustion will go on so far as to en¬
danger the breaking of the jar, by the approach of the in¬
flamed phosphorus.
In this process, a white dense vapour is produced, which
condenses on the inner surface of the jar in solid flakes. This
substance has strongly acid properties ; and, being formed by
the union of oxygen with phosphorus, is termed the phos¬
phoric acid.
The diminution of the volume of oxygen gas, by the com¬
bustion of other bodies, may be ascertained in a similar man¬
ner. When the substance employed is not easily set on fire, j
it is proper to enclose, along, and in contact with it, a small
bit of phosphorus, the combustion of which excites sufficient
heat to inflame iron-turnings, charcoal, &c. In the instance
of charcoal, however, though that substance undergoes com¬
bustion, no absorption ensues ; because, as will appear in the
sequel, the product is a gas, occupying exactly the same bulk
as the oxygen gas submitted to experiment.
IV. All bodies , by combustion in oxygen gas , acquire an ad¬
dition to their weight ; and the increase is in proportion to the '
quantity of gas absorbed , viz. about one third of a grain for
every cubic inch of gas.— 1 To prove this by experiment, requires
also a complicated apparatus.
But sufficient evidence of this fact may be obtained by the
following very simple experiment. Fill the bowl of a tobacco
SECT. II.
OXYGEN GAS.
HI
pipe with iron wire coiled spirally, and of known weight :
let the end of the pipe be slipped into a brass tube, which is
screwed to a bladder filled with oxygen gas : heat the bowl
of the pipe, and its contents, to redness in the fire, and then
force through it a stream of oxygen gas from the bladder. The
iron wire will burn ; will be rapidly oxydized ; and will be
found, when weighed, to be considerably heavier than before.
When completely oxydized in this mode, 100 parts of iron
wire gain an addition of about 30.
V. Every substance , caphble of union with oxygen , affords ,
by combustion , either an oxide , an acid , or an alkali.— When a
body, by being burnt in oxygen gas, affords a compound,
which has none of those qualities that characterize acids or
alkalies, we denominate this product an oxide. If we collect,
for example, the iron wire, which was burned in the last ex¬
periment, we shall find that it has lost all its metallic qualities,
and has become a brittle, dark-coloured substance totally des¬
titute of lustre and of taste, and termed an oxide of iron. But
if, instead of iron wire, we had burned a quantity of sulphur
in oxygen gas, over water, the result would have been that the
water, which confined the gas, would have become acid or
sour. Potassium, on the contrary (one of the new metals dis¬
covered by Sir H. Davy), would have yielded an alkali under
the same circumstances. Hence the extensive class of com¬
bustible bodies may be subdivided into three orders ; 1st, those
which afford oxides by combination with oxygen; 2dly, those
which yield acids ; and 3dly, those which give alkalies. In
many instances, however, a body is capable of passing through
the intermediate state of an oxide, before it is converted either
into an acid or an alkali.
VI. Oxygen gas supports , eminently , animal life. — It will be
found that a mouse, bird, or other small animal, will live four
or five times longer in a vessel of oxj^gen gas, than in one of
atmospherical air of the same dimensions.
VII. This effect seems connected with the absorption of oxygen
by the blood. — Pass up a little dark-coloured blood into a jar
partly filled with oxygen gas, and standing over mercury.
The gas will be in part absorbed, and the colour of the blood
will be changed to a bright and florid red. This change to
2
142
GASES.
CHAP. V.
red may be shown, by putting a little blood into a common
vial filled with oxygen gas, and shaking it in contact with
the gas.
i
SECTION III.
Chlorine Gas .
I. This gas may be formed by either of the following pro¬
cesses :
Process 1. Into a stoppered retort introduce eight ounces
of liquid muriatic acid, and four ounces of finely powdered
manganese, and apply the heat of a lamp. A gas will be pro¬
duced, which may be received, in the usual manner, over
water of the temperature of 80° or 90° Fahrenheit. From
the foregoing materials about 160 cubical inches of gas may
be obtained.
Process 2. Grind together in a mortar eight ounces of
muriate of soda (common salt) with three ounces of powdered
manganese; put them into a stoppered retort, and pour on
them four ounces of sulphuric acid, which have been diluted
previously with four ounces of water, and suffered to cool after
dilution. Or the proportions recommended by Thenard may
be employed, viz. 1750 muriate of soda, 450 oxide of man¬
ganese, water and sulphuric acid each 800. On applying a
gentle heat gas will be produced, as in Process 1. But as the •
gas is absorbed by contact with cold water, though not rapidly,
it should be received, when it is intended to be kept, in bot-;1
ties filled with, and inverted in, water of the temperature of
80° or 90° Fahr. and provided with accurately ground stop¬
pers. The stoppers must be introduced under water, while d!
the bottle remains quite full of the gas, and inverted, and no> :
water must be left in the bottle, along with the gas.
II. Chlorine gas has the following properties :
( a ) It has a yellowish green colour; and this property has sjl
suggested the name chlorine
(5) It has a pungent and suffocating smell. In experiments s
*
From pc>>»po?, green.
9
SECT. HI.
CHLORINE GAS,
143
on this gas, great care should be taken that it does not escape,
in any considerable quantity, into the apartment; for its action
on the lungs is extremely oppressive and injurious.
(c) It is heavier than common air (taking the statement of
Gay Lussac) in the proportion of 2470 to 1000 by experi¬
ment, or 24216 by calculation ; and 100 cubic inches should,
therefore, weigh 75*33 grains. Sir H. Davy finds them to
weigh between 76 and 77 grains, at a mean temperature and
pressure, which would make its specific gravity 2,5Q82.
(d) By a temperature of -j- 40° Fahr. it is reduced into a
liquid form, and is condensed on the sides of the vessel. But
if the gas be previously dried by exposure to muriate of lime,
it bears a cold of 40° below 0 without condensation *.
When a receiver, filled with this gas, not artificially dried,
is surrounded by snow, or pounded ice, the gas forms on its
inner surface a solid concretion, of a yellowish colour, resem¬
bling, in its ramifications, the ice which is deposited on the
surface of windows during a frosty night. By a moderate in¬
crease of heat, such as to 50° Fahrenheit, this crust melts into
a yellowish oily liquid, ^hich, on a farther elevation of tem¬
perature, passes to the state of a gas.
(e) Chlorine gas, in its ordinary state, destroys all veget-
i able colours. This may be shown by passing, into the gas
confined by water, a piece of paper stained with litmus, the
colour of which will immediately disappear. Hence the ap¬
plication of this gas to the purpose of bleaching, its power of
V effecting which may be shown by confining, in the gas, a
pattern of unbleached calico, which has been previously boiled
in a weak solution of caustic potash, and then washed in
water, but not dried. Chlorine gas, however, which has been
carefully dried by solid muriate of lime, and into which per-
r fectly dry litmus paper is introduced, produces no change of
; colour in the litmus, a sufficient proof that its bleaching power
depends on the presence and decomposition of water.
(f) This gas is absorbed by water; slowly, if allowed to
JStand over it quiescent, but rapidly when agitated.
1 . The best method of effecting the impregnation of water
* Sir 14. Davy, Phil, Trans. 1811, p, 30,
144?
eASES.
CHAP. V.
with this gas, is by means of a Woulfe’s apparatus, the bottles
of which should be surrounded by ice-cold water. The quan¬
tity of the gas, which water is capable of absorbing, appears,
from the concurrent testimony of Davy and Dalton, to be
twice its bulk. The former has lately remarked that water,
apparently saturated with chlorine by agitation with it in a
narrow vessel, takes up more of the gas when exposed to it
with a broad surface.
2. The watery solution, if perfectly free from common mu¬
riatic acid, has not the usual taste of an acid, but an astrin¬
gent one. Its purity from muriatic acid may be ascertained
hy a solution of nitrate of mercury, which is not precipitated
by pure chlorine.
3. The waitery solution has the colour and peculiar smell of
the gas, and has a similar property of discharging vegetable
colours. Hence it may be employed in bleaching.
4. When the watery solution of chlorine is exposed to a
temperature only a little above that of freezing water, the gas,
which is combined with it, separates in the form of a liquid, I
heavier than water.
5. Chlorine is not altered by the temperature of boiling
water ; for its solution may be raised in distillation, and again ;
condensed without change.
6. When the solution of chlorine in water is exposed to the
direct rays of the sun, oxygen gas is obtained, and the acid
passes to the state of muriatic acid.
Chlorine is susceptible of combination with various other
bodies, and the compounds possess, in many instances, re¬
markable properties. 1 hese will be made the subject of a
distinct chapter in a subsequent part of the work.
SECTION IV.
Nitrogen or Azotic Gas .
After separating, from any quantity of atmospherical air,
all the oxygen which it contains, there remains a gas which
was called by Lavoisier azotic gas0 a name applied to it in con-
i
SECT. IV.
145
NITROGEN GAS.
sequence of its unfitness for supporting animal life ; and de¬
rived from the Greek privative a and vita. This, however,
as being merely a negative property, has since been deemed
an improper foundation for its nomenclature: and the term
nitrogen gas has been substituted ; because one of the most
important properties of its base is, that by union with oxygen
it composes nitric acid. By this appellation, therefore, I shall
hereafter distinguish it.
1. Nitrogen gas may be procured, though not absolutely
pure, yet sufficiently so for the purpose of exhibiting its gene¬
ral properties, in any of the following manners : 1. Mix equal
weights of iron filings and sulphur into a paste with water,
and place the mixture, in a proper vessel, over water, sup¬
ported on a stand: then invert over it, a jar full of common
air, and allow this to stand exposed to the mixture for a day
or two. The air contained in the jar will gradually diminish,
as will appear from the ascent of die water within the jar, till
at last only about four 5ths of its original bulk will remain.
The vessel containing the iron and sulphur must next be re¬
moved, by withdrawing it through the water; and the remain¬
ing air may be made the subject of experiment.
2. A quicker process, for procuring nitrogen gas, consists
in filling a bottle, about one 4th, with the solution of nitrous
gas in liquid sulphate of iron, or with liquid sulphuret of
lime, and agitating it with the air which fills the rest of the
bottle. During the agitation, the thumb must be firmly placed
over the mouth of the bottle; and, when removed, the mouth
of the bottle must be immersed in a cup full of the same solu¬
tion, which will supply the place of the absorbed air. The
agitation, and admission of fluid, must be renewed, alternately,
i as long as any absorption takes place.
3. Atmospheric air, also, in which phosphorus has burned
► out, affords, when time has been allowed for the condensation
I of the phosphoric acid, tolerably pure nitrogen gas.
4. Azotic gas may be procured from the lean part of flesh
i meat (beef for example), which may be put into a gas bottle,
along with very dilute nitric acid. By a heat of about 100°,
the gas is disengaged, and may be collected over water. Its
VOL. i. l
146
GASES.
CHAP. V»
source has been satisfactorily traced to the animal substance?
no part of it proceeding from the nitric acid.
II. Nitrogen gas has the following properties :
1. It is not absorbed by water.
2. It is a little lighter than atmospheric air ? 100 cubic inches
being found by Sir H. Davy to weigh 30* *04 grains under a
pressure of 30 inches? and at the temperature of 55° Fahren¬
heit. At 60° Fahrenheit 100 inches weigh? therefore? 29*73
grains. According to Biot and Arajo? its specific gravity is
0*96913.
3. It immediately extinguishes a lighted candle? and all
other burning substances. Even phosphorus? in a state of
active inflammation, is instantly extinguished when immersed
in nitrogen gas. This is best shown by placing the burning
phosphorus in a tin cup, raised by a stand over the surface of
the water? and quickly inverting over it ajar filled with nitro¬
gen gas.
4. It is fatal to animals that are confined in it.
5. When mixed with pure oxygen gas? in the proportion
of four parts to one of the latter? it composes a mixture re¬
sembling atmospheric air in all its properties. Of this any¬
one may be satisfied? by mixing four parts of azotic gas with
one of oxygen gas, and immersing? in the mixture, a lighted
taper. The taper will burn as in atmospherical air.
Composition of Nitrogen .
That nitrogen is not an element, but itself a compound, ha&
been long suspected, and various attempts have been made to
discover its ingredients. Some of the facts, which have been
supposed to throw light on its nature, I shall reserve for the
chapter on ammonia, because they will be better understood
in connection with that subject.
Berzelius, from the combination of experiment with much
theoretical reasoning, has deduced, that nitrogen is com¬
pounded of oxygen and an unknown base, in the following
proportions * :
. . . i m ■ y.in -n m - . - • T-n-4ur g t--~ .
* 2 Thomson's Annals, 284.
SECT. IV. NITROGEN GAS.
Base .... 44.32 79.84 ...... 100.00
Oxygen . . 55.68 . 100 . 125.51
100 179.61 225.51
This base, it must be observed, however, is purely hypo*?
thetical ; and, as it has never yet been exhibited in a separate
State, we cannot at present know any thing of its properties.
Berzelius has proposed for it the name of nitricum.
A series of experiments to prove the composition of nitro¬
gen by synthesis, has been published in the 4th volume of Dr.
Thomson’s Annals, by Mr. Miers, of London. He attempted
to deprive water of part of its oxygen by transmitting it,
along with sulphureted hydrogen, through an ignited copper
tube ; by which process he obtained a mixture of oxygen and
nitrogen gases, in proportions the same as those constituting
atmospheric air. If no source of fallacy existed in the expe»
riment, it wogld follow that nitrogen is composed of oxygen
and hydrogen, with less oxygen than exists in water. But the
experiments, though ingeniously devised, require the most
careful repetition, before so important a conclusion can be
established ; and there is reason to suspect, from the nature of
the products, that atmospheric air must, by some means, have
found its way into the apparatus. It is remarkable, however,
that the proportions of the elements of ammonia, deduced by
Mr. Miers from his experiments, precisely agree with the
hypothetical proportions assigned by Berzelius, viz. 55.6 oxy¬
gen and 44.4 hydrogen per cent, in weight.
The experiments of Sir IT. Davy #, directed to the decom-?
position of nitrogen, on the presumption of its being an oxide,
have not been attended with any better success. Potassium
was ignited, by intense Voltaic electricity, in nitrogen gas ;
and the result was, that hydrogen appeared, and some nitro¬
gen was found deficient. This, on first view, would lead to
the suspicion, that nitrogen was decomposed. But, in sub-
sequent experiments, in proportion as the potassium was more
free from a coating of potash, which would introduce water,
so, in proportion, was less hydrogen evolved, and less nitron
* Phil. Trans. 1810,
p 2
148
GASES.
CHAP. V.
gen found deficient. The general tenor of these inquiries,
therefore, lends no strength to the opinion, that nitrogen is a
compound body.
SECTION V.
Atmospheric Air .
The air of our atmosphere, it appears, from the facts
stated in the preceding section, is a mixture of two different
gases, viz. oxygen gas and azotic gas. The former of these
seems to be the only ingredient on which the effects of the air,
as a chemical agent, depend. Hence combustible bodies
burn in atmospheric air, only in consequence of the oxygen
gas which it contains ; and, when this is exhausted, air is no
longer capable of supporting combustion *. Its analysis is
most satisfactorily demonstrated by the action of heated mer¬
cury, as explained by Lavoisier, in the third chapter of his
Elements of Chemistry. By exposure, during 12 days, to
mercury heated in a retort, a given quantity of atmospheric
air was found to be diminished in bulk, and to have lost its
property of supporting combustion. The mercury, also, had
suffered a considerable change ; a part of it was no longer a
shining fluid metal ; but was changed into red scaly particles ;
and its weight was, also, increased. These red particles were
collected, and distilled in a retort; by which operation a
quantity of oxygen gas was evolved, precisely equal in bulk
to what the air had lost in the first part of the experiment.
These results afford the most satisfactory evidence, that the
air of our atmosphere is composed of two distinct fluids.
The one is capable of yielding its base to mercury; and,
when separate, is eminently adapted to the support of com¬
bustion and of animal life; the other is not absorbable by
mercury, and is destitute of both those important qualities.
The details of this method of analyzing atmospheric air
* Certain combustible bodies even cease to burn in atmospheric air, long
before its oxygenous portion is consumed, for reasons that will hereafter be
given.
SECT. V.
ATMOSPHERIC AIR.
149
I omit on account of the extreme tediousness of the process.
Sufficient evidence of its composition may be obtained, how¬
ever, much more expeditiously ? by the following experiments.
I. Bum a little sulphur or phosphorus, in the manner de¬
scribed, sect. ii» substituting, for oxygen gas, common atmo¬
spherical air. The combustion will, in this instance, be less
vivid; will cease sooner; and the absorption, when the vessels
have cooled, will be much less considerable than in the former
case.
The phosphorus, however, will have absorbed the whole
of the oxygen gas contained in the air submitted to experi¬
ment; and hence it may be employed for measuring the quan¬
tity of oxygen gas in a given bulk of atmospherical air. This
may be accomplished, either by its slow or rapid combustion.
Berth ollet proposes* to expose a cylinder of phosphorus, fast¬
ened to a glass rod, in a narrow glass vessel, graduated into
equal parts, and standing full of air over water. (See fig. 24.)
The phosphorus immediately begins to act without visible com¬
bustion on the included air; and in six or eight hours its effect
is completed. The residuary azotic gas has its bulk enlarged
about one 40th, by absorbing a little phosphorus; and for
this allowance must be made in measuring;; the diminution.
In the eudiometer of Seguin, the rapid combustion of phos¬
phorus is employed with the same view. A glass tube, open
at one end only, about an inch in diameter, and eight or ten
high, is filled with, and inverted in, mercury. A small bit
of phosphorus, dried with blotting paper, is then introduced,
and, by its inferior specific gravity, rises to the top of the
tube where it is melted, by bringing a red-hot poker near to
the outer surface of the glass. When the phosphorus is lique¬
fied, a measured portion of the air to be examined is ad¬
mitted, by a little at once, into the tube. The phosphorus
inflames at each addition, and the mercury rises. When all
the air under examination has been added, the red-hot poker
is again applied to ensure the completion of the process, and
the residuary gas is transferred into a graduated measure,
where its bulk is carefully ascertained. In this instance,
* Annales de Chimie, xxiv. 78.
&ASES.
CHAP. Vi
about one 40th the volume of the residuary gas is to be de¬
ducted from the apparent quantity of azotic gas, because, in
this case also, a small portion of phosphorus is dissolved by
the latter, and occasions a trifling expansion* With this
deduction, atmospheric air loses pretty accurately 21 parts
out of every 100; and contains, therefore, 21 per cent, of
oxygen, and 79 of azote by measure *. And it is remarkable,
that no appreciable difference exists between the proportions
of oxygen and azote in the atmospheres of distant places ;
from which it appears, that the purity and salubrity of air
depend on some other circumstances than the proportion of
these its chief elements.
II. The inferior fitness of atmospherical air to that of oxy¬
gen gas, for supporting combustion, may be shown, also, by
a comparative experiment with two candles. Provide a cir¬
cular piece of lead, three inches diameter, and half an inch
thick, from the centre of which proceeds a perpendicular iron
wire, six or eight inches high ; to the end of this wire fasten
a piece of wax taper. Set the candle, supported by its stand,
on the shelf of a pneumatic cistern; and place, also, the
conducting pipe from the bladder (e, fig, 41), in the position
shown by the figure; the cock d9 however, being shut. Then,
having the syphon g in the inverted position shown in the
plate, sink the whole apparatus into the water. Part of the
air in the jar a will escape through the syphon, and will be re¬
placed by water. When we have left, in the jar, the proper
quantity of air, the syphon must be removed, and the jar re¬
turned to its place. The level of the water will now be con¬
siderably higher within than without the receiver; and its
height must be noted. On passing a succession of electrical
sparks from the conducting wire to the bent pipe5 and opening
the cock d from the bladder filled with hydrogen gas, we shall
have a small flame, which is to be extinguished as soon as, by
its means, we have lighted the candle. The candle may be
suffered to burn till it is extinguished ; and the duration of its
* Various other methods of analyzing atmospherical air will be described
in the course of the work. References to them may be found in the Index,
article Eudiometer*
SECT. V.
ATMOSPHERIC AIR.
151
burning, and the diminution it occasions in the air, are to be
noted. When the combustion is repeated in the same man¬
ner, but with the substitution of oxygen gas, it will be found
to last considerably longer, and the diminution of volume in
the gas will be much greater.
The same fact may be demonstrated, but less accurately,
by a simple apparatus. Provide two jars, each two inches
in diameter, and 12 inches long, and each having a neck at
the top with a compressed bladded tied upon it. Fill one of
the jars, leaving the bladder empty, with oxygen gas; and, at
the same instant, with the aid of an assistant, invert both jars
over the burning candles, keeping the oxygen gas in its place
till the jar is inverted, by a piece of pasteboard. In the com¬
mon air, the candle will soon be extinguished ; but that con¬
fined in oxygen gas will burn with much greater splendour,
and will continue burning long after the other is extinguished.
On the first impression of the dame, a quantity of expanded
gas will rise into each bladder, which is to be pressed out at
the close of the experiment, in order that the absorption may
be compared in both cases. The diminution in the jar of
oxygen gas will be found greatly to exceed that of the common
air.
III. Take two tubes, each a few inches long, closed at
one end, and divided into 100 aliquot parts. Fdl the one
with atmospherical air, the other with oxygen, gas, and invert
them in two separate cups filled with a solution of sulphuret
of potash. The sulphuret will ascend gradually within the
tube of common air, till, after a few days, about four 5ths of
its original volume will remain ; but, in that containing oxy¬
gen, it will ascend much higher, and if the gas be pure, will
even absorb the whole.
The explanation of this fact is, that liquid sulphuret of
potash has the property of absorbing oxygen, but not nitrogen.
It therefore acts on atmospheric air only as long as any oxygen
gas remains, and may be employed as a means of ascertaining
the quantity of this gas in the atmosphere at different times,
and in distant places. An improved instrument thus gra-
* See Nicholson’s Philosophical Journal, 4to. i. 268; or Xilloch’s
Philosophical Magazine, iii. 171.
152
GASES.
CHAP. V.
dilated, has been employed by Guyton as an Eudiometer *.
But an apparatus, of much greater simplicity, and facility of
application, is that of Professor Hope of Edinburgh, an¬
nounced in Nicholson’s Journal, 8vo. iv. 1510. It consists of
a small bottle, of the capacity of 20 or 24 drachms (fig. 20,
pi. ii), destined to contain the eudiometric liquid, and having
a small stopper at b. Into the neck of the bottle a tube is
accurately fitted, by grinding, which holds precisely a cubic
inch, and is divided into 100 equal parts. To use the appa¬
ratus, the bottle is first filled with the liquid employed, which
is best prepared by boiling a mixture of quicklime and sulphur
with water, filtering the solution, and agitating it for some
time in a bottle half filled with common air. The tube, filled
with the gas under examination (or with atmospherical air,
when the quality of this compound is to be ascertained), is
next to be put into its place; and, on inverting the instru¬
ment, the gas ascends into the bottle, where it is to be
brought extensively into contact with the liquid by brisk agi¬
tation. An absorption ensues; and, to supply its place, the
stopper b is opened under water, a quantity of which rushes
into the bottle. The stopper is replaced under water; the
agitation renewed ; and these operations are performed alter¬
nately, till no farther diminution takes place. The tube a is
then withdrawn, the neck of the bottle being under water,
and is held inverted in water for a few minutes; at the close
of which the diminution will be apparent. Its amount may
be measured by the graduated scale engraved on the tube.
To the eudiometer of Hr. Hope there are, however, a few
objections. If the tube a and the stopper b are not both very
accurately ground, air is apt to make its way into the instru¬
ment, to supply the partial vacuum, occasioned by the ab¬
sorption of oxygen gas. This absorption occasions a dimi¬
nished pressure within the bottle; and, consequently, towards
the close of each agitation, the absorption goes on very slowly.
Besides, the eudiometric liquid is constantly becoming more
dilute by the admission of water through b. To obviate all
these difficulties, I have substituted for the glass bottle, one
* Other eudiometers will be described hereafter.
SECT V.
153
ATMOSPHERIC AIR.
of elastic gum, as shown by fig. 21, b. The tube a is accu¬
rately ground into a short piece of very strong tube of wider
bore, as shown at c, the outer surface of which is made rough
by grinding, and shaped as represented, that it may more
effectually retain the neck of the elastic bottle when fixed by
a string. This instrument is used, in every respect, in the
same way as Dr. Hope’s. The only difficulty is, in returning
the whole of the residuary gas into the tube; but the art of
doing this will be acquired by practice.
An ingenious modification of the eudiometer, which ena¬
bles us to measure an absorption of only T-Anyth part of the
gas employed, is described by Mr. Pepys, in the Philoso¬
phical Transactions for 1807? or Philosophical Magazine,
xxix.
IV. Atmospheric air supports animal life , only in consequence
of the oxygen gas which it contains. — Air, after having been
received into the lungs, and again expired, is found to have
lost a considerable part of its oxygen, viz. from 10 to 12 per
cent. It proves fatal to animals, however, long before this
ingredient is wholly exhausted ; and hence it appears, that a
considerable portion of oxygen gas is necessary to fit the air
for supporting respiration. As tiie analysis of expired air re¬
quires an acquaintance with another gas, not hitherto de¬
scribed, viz. carbonic acid, its examination will be postponed
to a future occasion.
V. Atmospheric air is diminished in volume by animal respi¬
ration.- — This may be shown by repeating a very simple expe¬
riment, originally contrived by Mayow. He confined a mouse
in a small glass jar, and tied the jar over, quickly and firmly,
with moistened bladder. The heat of the animal first ex¬
panded the air, and rendered the bladder convex outwards ;
but when the animal after death had become cold, the bladder
exhibited a hollow surface, proving that the air within was
diminished in its bulk.
The exact amount of the diminution may be shown, by con¬
fining a mouse, over water, in a graduated jar, furnished with
a stop-cock, and containing common air. As the heat of the
animal, however, would occasion the expulsion of part of the
air, it is expedient, on first depressing the jar into waiter, to
2
154*
GASES.
CHAP. V*
open the cock, through which a part of the air will escape :
the cock is then to be shut, and the height of the water within
to be accurately noted. At first, the level will be depressed,
in consequence of the expansion of the air by the warmth of
the animal ; but, after its death, a considerable diminution
will be observed.
VI. The weight of 100 cubic inches of atmospheric air, at
60° Fahrenheit and 30 inches barometer, is said by Mr. Kir-
wan to be 30.92 grains. Sir H. Davy states it, when under
the same pressure, but at 55° Fahrenheit, to be 31.10 grains,
from which may be deduced that with the temperature and
pressure assumed by Mr. Kirwan, 100 inches would weigh
30.78 grains. Under the same circumstances, Sir George
Shuckburgh’s experiments fix its weight at 30.5 grains ; and
this is probably the most correct determination.
SECTION VI.
Hydrogen Gas*
The most simple form, in which hydrogen has hitherto
been obtained, is in that of a gas, or in a state of union with
caloric, and perhaps with electricity and light. From this
combination we are not able to separate it, except by availing
ourselves of the affinity of some other substance, in which case
the hydrogen separates from the caloric, and forms, with the
body which has been added, anew combination. Of its nature,
we know but little ; but as it has not vet been resolved into
any more simple form, it is still arranged among elementary
bodies. From the recent experiments of Sir FI. Davy (which
will be described under the article ammonia), it appears not
improbable that hydrogen is a metallic body.
The most important compound of hydrogen, and the only
one which will be noticed at present, is that which it affords
by union with the base of oxygen gas. It is on its affinity for
this base that all the properties depend, which are illustrated
by the following experiments. Much of the force of this at¬
traction, it will appear probable from the sequel, depends on
3
SfeCT. Vi. HYDROGEN GAS; 15$
its being in a state of opposite electricity to oxygen ; for, in
common with all inflammable substances, it is naturally in a
state of positive electricity.
I. To procure hydrogen gas$ let sulphuric acid, previously
diluted with five or six times its weight of water, be poured
on iron filings, or on small iron nails ; or (what is still better)
pour sulphuric acid, diluted with eight parts of water, on
zinc *, granulated by pouring it melted into cold water, and
contained in a gas bottle or small retort. An effervescence
will ensue, and the escaping gas may be collected in the usual
manner. An ingenious apparatus for obtaining it instanta¬
neously in a laboratory is described by Gay Lussac, in the
5th vol. of Ann. de Chirn. et Phys. p. 300. Its construction
can scarcely be understood, without the plate which accom¬
panies it.
Hydrogen gas, thus obtained, is not, however, to be consi¬
dered as absolutely pure. An observation of Mr. Cuthbertson
long ago rendered it probable that, when disengaged by zinc,
it contains a portion of that metal 5 and, when generated by
means of iron, it is apt to contain a little carbureted hydro¬
gen. Mr. Donovan has also shown t? that, when procured
from zinc and dilute sulphuric acid, it is contaminated with
sulphureted hydrogen and carbonic acid ; and he recom¬
mends that to obtain pure hydrogen, we should first agitate
common hydrogen with lime-water during a few minutes, next
with a little nitrous acid, afterwards with solution of green
sulphate of iron, and finally with water. It appears to me,
however, that as the only impurities, discovered by Mr. Do¬
novan in hydrogen gas, were carbonic acid and sulphureted
hydrogen, they might be equally well removed by the simple
process of washing the gas either with lime-water or with a
solution of caustic potash.
II. This gas has the following properties :
1 . It remains permanent over water , or is not absorbed in a
proportion exceeding JR-th the bulk of the water.
2. As commonly procured , it has a disagreeable smell ; but
_ _ _ _ _ ■ _ _ i
* Zinc may be purchased at the brass-founders or copper-smiths, under
the name of speltre.
f Phil. Mag. xlviii. 138.
156
GASES.
CHAP. V.
pure hydrogen gas was found by Mr. Donovan to be free
from all odour.
3. It is inflammable. This may be shown by the following
experiments :
(a) Fill a small jar with the gas, and, holding it with the
mouth downwards, bring the gas into contact with the flame
of a candle. The air will take fire, and will burn silently with
a lambent flame.
(5) Fill with this gas a bladder which is furnished with a
stop-cock, and with a small pipe, of diameter less than that of
a common tobacco pipe. Press the air out through the pipe,
and, on presenting a lighted candle, the stream will take fire.
If this apparatus cannot be procured, a very simple contriv¬
ance will answer the purpose: break off part of an eight-
ounce vial, within an inch or two from the bottom, by setting
fire to a string tied round it, and moistened with spirit of tur¬
pentine. The vial will then resemble ajar with an open neck
at the top. Next bore a small hole through a cork that fits
the neck ox the vial, and insert in it part of a common tobacco
pipe, which may be fixed into the neck of the bottle, by a
cement of resin and bees- wax. Then fill the bottle with water,
and hold it, with the thumb pressed down on the aperture of
the pipe, while hydrogen gas is passed into it. When the
bottle is full of gas, remove the thumb, press the bottle down
into the water, and, on the approach of a candle, the stream
of air from the pipe will take fire.
Persons, who are provided with the jars represented pi. ii.
fig. 22, a , may screw to the cock a brass pipe with a small
aperture. On pressing the jar, filled with hydrogen gas, into
the water, and opening the cock, the gas will be forced out in
a stream, which may be set on fire. On this principle are
founded the artificial fireworks without smell or smoke. They
consist of pipes, having variously sized apertures, some of
which have a rotatory motion.
(c) In a strong bottle, capable of holding about four ounces
of water, mix equal parts of common air and hydrogen gas.
On applying a lighted candle, the mixture will burn, not
silently, as in experiment ( a ), but with a sudden and loud ex¬
plosion. If a larger bottle be used, it should be wrapped
SECT. VI.
HYDROGEN GAS.
157
round with a handkerchief, to prevent the glass from doing
any injury, in case the bottle should be burst *.
[d) The same experiment may be repeated with oxygen gas,
instead of atmospherical air ; changing the proportions, and
mixing only one part of oxygen gas with two of hydrogen.
The report will be considerably louder. The bottle should
be a very strong one, and should be wrapped round with cloth,
to prevent an accident.
(e) The same experiment may be made over water, by means
of the electric spark. Procure a strong tube, about three
quarters of an inch diameter, and 12 inches long, closed at
one end (plate ii. fig. 29, b ). About a quarter or half an inch
from the sealed end, let two small holes be drilled, opposite to
each other, and into each of these let a brass conductor be
cemented, so that the two points may be distant from each
other within the tube, about one 8th of an inch. An appa¬
ratus, serving the same purpose, and much more easily con¬
structed, may be formed by hermetically' sealing a piece of
brass wire, or still better platina wire, into the end of a glass
tube (fig. 29, a). With this conductor, an interrupted circuit
may be formed, by introducing into the tube a longer wire,
one end of which terminates one 10th of an inch from the
upper one, while the other extends beyond the aperture of
the tube. (See fig. 84.) Into this tube, standing over water,
pass about half a cubic inch of a mixture of hydrogen and
oxygen gases ; in the proportion of two measures of the former
to one of the latter. Hold the tube firmly, and pass an elec¬
tric spark through the mixed gases. For relieving the shock,
which is sometimes considerable on firing, an ingenious con¬
trivance of Sir H. Davy may be employed. It is described in
the Philosophical Magazine, xxxi. 3. An immediate explo¬
sion will take place ; after which the gases, if pure, and in the
proper proportion, will be found to have disappeared entirely.
It has been asserted by Grotthuss, that a mixture of two
measures of hydrogen gas with one of oxygen, cannot be in¬
flamed by the electric spark, when expanded to 16 times its
* These experiments may also be made advantageously, by means of an.
apparatus sold under the name of the inflammable air-pistol.
158
GASES.
CHAP. V,
volume by diminished pressure ; nor, when dilated by heat to
only six times its volume. In the latter case, even a lighted
taper does not kindle the mixture ; but water is formed silently
by a continued succession of electric sparks *.
It is rarely, however, that oxygen and hydrogen gases can
be used in such a state of purity as to leave absolutely no re¬
siduum. To determine, indeed, the purity either of the oxygen
or hydrogen gas employed, it is sometimes necessary so to adjust
their proportions, that the whole mixture may not be con¬
densed by firing. If, for example, we wish to know the purity
of a quantity of oxygen gas , we are to use about three times its
bulk of hydrogen. Let us suppose that 100 measures of oxy¬
gen are detonated with 300 of hydrogen gas, and that the
total 400 is reduced by firing to 130; the diminution of
volume will be 270. This number, divided by three, gives 90
for the quantity of oxygen ; that is, the oxygen employed must
have contained 10 per cent, of nitrogen, or of some foreign
gas not condensible by hydrogen.
If atmospherical air be employed, a diminution, though not
equal in amount, will be produced by the union of the hydro¬
gen with the oxygen gas contained in the air ; and if a suffi¬
cient quantity of hydrogen gas be employed, the whole of the
atmospheric oxygen will thus be removed. On this principle
is founded the Eudiometer of Volta, which may be con¬
structed, by graduating either of the tubes already described,
into equai parts f. If, in one of these tubes, we mix 300 parts
of common air, and 200 of pure hydrogen gas, there will re¬
main, after the explosion excited by passing an electric spark
between the two wires, about 305 measures. There will, there¬
fore, have been a diminution of 195 measures, of which pretty
exactly one 3d may be estimated to be pure oxygen. In
this instance, therefore, 65 of oxygen have been lost by 300
of air, or 2 1 and a fraction per cent.
The general rule for ascertaining the purity of atmospheric
air by hydrogen gas, may be stated as follows : Add to three
measures of the air under examination, two measures of pure
* 82 An. de Chimie, 37.
f A Volta’s Eudiometer, invented by Gay Lussac, is described in An*
ide Chim. et Phys. iv. 188.
SECT. VI.
HYDROGEN GAS.
1 59
hydrogen gas ; inflame the mixture by electricity ; observe
the diminution when the vessel has cooled ; and, dividing its
amount by three, we obtain pretty nearly the quantity of
oxygen gas which has been condensed.
In the reverse process, i. e. in determining the purity of hy¬
drogen gas , we mix it with more oxygen gas than is required
for saturation. Suppose that to 100 of hydrogen gas we add
100 of oxygen, and that 80 measures remain after detona¬
tion. The diminution will have been 120 measures; and,
of these, two 3ds or 80 measures are hydrogen. Hence
the inflammable gas, under examination, must contain 20 per
cent, of some other gas, which is most probably nitrogen.
In this way, we determine the proportions of hydrogen and
nitrogen in any mixture composed of those two gases only.
(f) The diminution of hydrogen and oxygen gases, by the
union of their bases, may be shown also by their slow com¬
bustion. Fill a tall jar with oxygen gas, and fill also, with
hydrogen gas, a bladder furnished with a stop-cock, and with
a long brass pipe bent like the letter S, and drawn out to a
fine point (plate iv. fig. 41). On pressing the bladder, a
stream of gas will issue from the pipe, which may be set on
fire, and brought cautiously under the tall inverted jar of
oxygen gas. By this contrivance, the stream of hydrogen gas
will be burnt in a confined portion of oxygen gas ; and, on
continuing the combustion a sufficient length of time, the wa¬
ter will be seen to rise gradually within the jar. On the first
impression of the heat, indeed, a quantity of gas will escape
from the jar, which will render it difficult to ascertain what
degree of absorption has actually taken place. But this loss
may be prevented, by using a jar with a neck at the top, to
which a compressed bladder is firmly tied. The expanded
air, instead of escaping through the water, will now fill the
bladder at the top ; and, when the experiment has closed, and
the vessels have cooled, it may be ascertained, by pressing out
the gas from the bladder, what quantity of oxygen gas has
been consumed.
The same experiment may be more accurately and ele¬
gantly made, with the assistance of an apparatus, which I
have described in the Philosophical Transactions for 1808,
160
GASES.
CHAP. Vi
The description cannot be understood without the plate, which
is there given, and which has been copied into the Philoso¬
phical Magazine, xxxii. and Nicholson’s Journal, xxi. The
fact may, also, be shown by substituting, for the bladder
(e, fig. 41), a small gazometer, containing a measured quan¬
tity of hydrogen gas. Let the bent pipe be screwed on the
cock of the gazometer ; and over its open end, placed perpen¬
dicularly, invert ajar of oxygen gas. This jar must be pro¬
vided at the top with a metallic conductor, screwed into a
brass cap, as represented in fig. 41 ; which shows also the
level of the water within the jar, attained by means of a sy¬
phon. After noting the height of the water within, let a rapid
succession of electric sparks be passed between the two con¬
ductors ; and, on opening the cock at this instant, the stream
of oxygen gas will be inflamed. The end of the pipe must
then be so far depressed, that the cement of the brass cap
may not be melted by the Same ; and the outer surface of the
top of the vessel should be kept cool. When the gas is first
lighted, the oxygen gas will be suddenly expanded ; but, pre¬
sently, a rapid diminution will go on, till the water rises above
the end of the pipe, and extinguishes the flame. If pure oxy¬
gen gas be employed, it will be found, after the experiment,
uninjured in its quality, and will support the combustion of
burning bodies as 'well as before.
When the above experiment is made, with the substitution
of common air for oxygen gas, a diminution takes place, but
much less considerable, viz. not amounting to one 6th of the
original bulk of the gas.
O O
(g) When a stream of hydrogen gas is burned under a tube,
18 or 24 inches long, a musical sound is produced. The ex¬
periment may be made in the following manner:
Into a glass bottle are put iron filings and sulphuric acid,
diluted with five or six parts of water; and a cork is fitted
into the neck, through which a glass tube is passed, having its |j
upper extremity drawn out to a capillary bore. By setting
fire to the hydrogen gas *, which escapes from this extremity,
* The gas must not be inflamed, till it has been produced for some time, :
and has expelled all the common air of the bottle; otherwise an explosion i
will happen, and the bottle will be burst, with some danger to the operator.
SECT. V.
HYDROGEN GAS.
161
a continued current or jet of flame is produced, which is
allowed to pass into a tube either of glass, earthenware, or
metal. If the tube be not too large, the flame becomes smaller
as it is depressed ; and when the tube covers the flame to a
considerable depth, very clear sounds are produced. But, on
the contrary, if the tube be too narrow, the flame will be ex¬
tinguished; and, in proportion as the tube is enlarged, the
sound diminishes : so that there is a certain limit at which it
totally ceases. The same happens when the tube is too long.
The sounds may be raised at pleasure, by either using tubes
of various figures or dimensions, or made of different sub¬
stances *.
(h) It has been discovered by M. Biot that a mixture of
hydrogen and oxygen gases may be made to explode by me¬
chanical compression. A mixture of these two gases was in¬
troduced into a strong metallic syringe, furnished with a glass
bottom, and a sudden stroke given to the piston. An ex¬
tremely brilliant light appeared, accompanied with a loud de¬
tonation ; and the glass bottom was forcibly driven out. The
repetition of this experiment, it is obvious, must be attended
with some difficulty and danger f . The heat given out by the
sudden compression of the gases is probably the cause of the
combustion which is excited.
The combustion of hydrogen and oxygen gases was many
years ago successfully applied by Mr. Hare of Philadelphia to
the purpose of exciting an intense heat by the blow-pipe.
The peculiar construction of the apparatus cannot be under¬
stood without a plate, which may be seen in the Annales de
Chimie , tom. xlv. or in the 14th volume of the Philosophical
Magazine. It may be sufficient here to state, that the gases
are contained each in a separate gasholder ; that they are ex¬
pelled by the pressure of a column of wrater obtained by
lengthening the pipe b , fig. 36 ; and that their mixture does
not take place, till they nearly reach the aperture of the pipe,
at the extremity of which they are inflamed. This last pre¬
caution is of considerable importance, because a violent and
* See Nicholson’s Journal, 8vo. i. 129, and iv. 23.-
f See Nicholson’s Journal, xii. 212.
M
VOL. I.
1 62
GASES.
CHAP. V.
dangerous explosion would otherwise happen. To guard the
more effectually against this accident, it is adviseable to affix a
valve, opening outwards, in the pipe proceeding from each
gasholder, just before the junction of the two.
The power of iiydrogen and oxygen gases to produce an
intense degree of heat, has lately been much increased, in
consequence of a suggestion of Mr. Newman to Professor
Clarke of Cambridge, that the gases should be previously
mixed, then condensed into a metallic reservoir, and made to
pass through a capillary tube before being set on fire *. The
temperature thus produced was found adequate to the instan¬
taneous fusion of the most refractory substances. Platinum,
for instance, was not only immediately melted, but set on fire
and consumed like iron wire in oxygen gas, with vivid scintil¬
lation. Considerable danger, however, arises to the operator,
from the liability of the condensed gases to explode and burst
the apparatus. Several expedients have been tried for the
purpose of obviating this risk, the most effectual of which,
suggested by Professor Gumming, consists in interposing, be¬
tween the flame and the main reservoir of gases, a cylinder
containing a little water or oil, through which, by means of a
valve at the bottom, the gas is allowed to pass f . All, there¬
fore, that can happen is the explosion of the mixed gases be¬
tween the inflamed jet and the surface of the oil or water,
where the quantity is not sufficient to occasion any serious
mischief. The more effectually to guard against danger, Dr.
Clarke has since, on the suggestion of Dr. Wollaston, inter¬
posed a fagot of capillary tubes of the smallest possible dia¬
meter, between the stop-cock, and the orifice of the pipe at
which the gases are inflamed $ . Additional safety may, also,
be given to the apparatus by interposing, between the operator
and the reservoir, a strong screen, through which the piston
rod of the syringe may be worked horizontally, and the flame
may thus be kept up for a length of time proportionate to the
* Journal of Science, &c. ii. 104.
t Journal of Science, & c. ii. 379, where a plate of the improved appa¬
ratus is given.
I Thomson's Annals, ix. 327.
SECT. V.
HYDROGEN GAS.
16$
size of the reservoir, from which the mixed gases are drawn
This modification of the instrument renders it applicable to
some of the arts, in which not only an intense but a long con¬
tinued heat is required.
4. Hydrogen gas , though inflammable itself, extinguishes
burning bodies,-— Bring an inverted jar, filled with this gas,
over the flame of a candle; and suddenly depress the jar, so
that the lighted wick may be wholly surrounded by the gas.
The candle will immediately be extinguished.
5. It is fatal to animals.—' This may be shown by confining,
in the gas, a mouse, or other small animal.
6. It is considerably lighter than atmospherical air.- — One
hundred cubic inches, the barometer being 30 inches, and the
thermometer 60°, weigh, according to Kirwan, 2.613 grains;
according to Lavoisier, 2.372 grains; and according to Four-
croy, Vauquelin, and Seguin, 2.75 grains. The recent de¬
termination of Sir H. Davyf is, that 100 cubic inches at 30.5
barometer, and 51° Fahrenheit, weigh 2.27 grains. Messrs.
Biot and Arago ascribe to it the specific gravity of 0.07321.
(a) Let a jar filled with this gas stand, for a few seconds,
with its open mouth upwards. On letting down a candle, the
gas will be found to have escaped.
(t) Place another jar of the gas inverted, or with its mouth
downwards. The gas will now be found to remain a short
time in the jar, being prevented from escaping upwards by the
bottom and sides of the vessel.
(c) Fill, with hydrogen gas, a bladder furnished with a
stop-cock ; and adapt to this a common tobacco pipe. Dip
the bowl of the pipe into a lather of soap, and, turning the
cock, blow up the lather into bubbles. These bubbles, in¬
stead of falling to fehe ground, like those commonly blown by
children, will rise rapidly into the air. On this property of
hydrogen gas, is founded its application to the raising of bal¬
loons.
(d) The experiment may be varied by filling the bladder
with a mixture of two parts of hydrogen gas and one of oxy-
* Thomson’s Annals, x. 373. Other improvements of the apparatus are
described in the same work, x. 366.
f Phil. Trans. 1810.
164
GASES.
CHAP. V.
gen gas. Bubbles, blown with this mixture, take fire on the
approach of a lighted candle, and detonate with a loud re¬
port. It is proper, however, not to set them on fire, till they
are completely detached from the bowl of the pipe ; otherwise
the contents of the bladder will be exploded, with consider¬
able danger to the operator.
In this place a property of hydrogen gas may be described,
which it possesses in common with all other a'eriform bodies,
viz. a tendency to diffusion through any other elastic fluid,
with which it may be brought into contact. Common or in¬
elastic fluids are capable of remaining in contact with each
other for a long time without admixture. Thus if we half fill
a wine glass with spirit of wine tinged with any colouring in¬
gredient, and then, by means of the dropping tube, fig. 15,
introduce under it a quantity of water, the spirit floats on the
water, and the two surfaces remain perfectly distinct, pro¬
vided we carefully avoid agitation or unequal changes of tem¬
perature. But this is not the case with elastic fluids or gases,
which, it has been discovered by Mr. Dalton *, penetrate
each other, and become thoroughly mixed under all circum¬
stances. The fact, with respect to hydrogen and oxygen gases,
may be proved, by a very simple apparatus.
Provide two glass vials, each of the capacity of about an
ounce measure, and also a tube open at both ends, 10 inches
long and one 20th inch bore. At each end, the tube is to be
passed through a perforated cork, adapted to the necks of the \
vials. Fill one of the bottles with hydrogen gas, and the other
with oxygen gas ; place the latter on a table with its mouth
upwards, and into this insert the tube secured by its cork. .
Then, holding the hydrogen bottle with its mouth downwards, ,
fit it upon the cork at the top of the tube. The two bottles,,
thus connected, are to be suffered to remain in this perpen¬
dicular position. After standing two or three hours, separate;
the vials, and apply a lighted taper to their mouths, when it
will almost certainly occasion an explosion in each. The 2!
hydrogen gas, though nearly 15 times lighter than the oxygen,
must, therefore, have descended through the tube from the j
* Manchester Memoirs, vol. i. new series.
SECT. V.
HYDROGEN GAS.
165
upper into the lower vial ; and the oxygen gas, contrary to
what might have been expected from its greater weight, must
have ascended through the tube, and displaced the lighter
hydrogen.
Experiments of this kind, it has been shown by Mr. Dalton,
may be extended to all the other gases ; but to prove the
effect, tests of a different kind are necessary, which require a
previous knowledge of the properties of these gases. They
tend to establish the conclusion, that a lighter elastic fluid can -
not remain upon a heavier without an admixture of the two .
166
CHAPTER VI.
OP THE COMPOSITION, DECOMPOSITION, AND PROPERTIES
OF WATER.
SECTION I.
Synthesis , or Composition , of Water.
In chap. v. sect. v. it was stated, that oxygen and hydrogen
gases, when fired over water, in the proper proportion, wholly
disappear. To ascertain the nature of the product thus
formed, the experiment must be repeated over mercury, in a
similar manner, by means of the detonating tube (pi. ii. fig.
28). When this is done repeatedly, it is found that the pro¬
duct of the combustion is that well known fluid, water, which
is thus proved to be composed of two elementary ingredients.
The water, produced in this mode, is not, however, to be
considered as a compound of the two gases, but only of their
bases ; for the light and caloric, which constituted the gases,
escape, in considerable part, during the combustion. Every
gas, it must be remembered, has at least two ingredients ; the
one, gravitating matter, which, if separate, would probably
exist in a solid or liquid form ; the other, an extremely subtile
fluid, termed caloric. In the example before us, caloric (and
perhaps electricity and light) is a common ingredient both of
hydrogen and oxygen gases ; but the twro gases differ in having
different bases. The basis of the one is called hydrogen, of
the other oxygen ; and water may, therefore, be affirmed to
be a compound, not of hydrogen and oxygen gases , but of
hydrogen and oxygen. Its composition may be proved in two
modes, by synthesis, i. e. by joining together its two element¬
ary ingredients ; and by analysis, in other words, by separat¬
ing the constitutent parts of water, and again exhibiting them
in a distinct form.
SECT. Io
SYNTHESIS OF WATER.
167
I. Fill, with hydrogen gas, a bladder, furnished with a
stop-cock and bent pipe (fig. 41, e), as in the last chapter.
Then pour into a shallow earthen dish as much quicksilver as
will about half fill it, and invert over this a glass bell, full of
common air and perfectly dry. Expel the hydrogen gas
through the pipe ; light the stream, and bring it under the
glass bell, by raising this, and depressing it into the mercury,
as soon as the inflamed gas is introduced. A portion of air
will escape, at first, in consequence of the rarefaction. As
the combustion continues, water will form, and will condense
on the sides of the glass. This water is produced by the union
of hydrogen with the oxygen contained in atmospheric air.
II. Those persons who are not possessed of a sufficient
quantity of quicksilver to repeat the above experiment, may
substitute the following : procure a large glass globe, capable
of holding three or four quarts, and having two openings,
opposite to each other, which may be drawn out for a short
distance, like the neck of a retort. Inflame the stream of
hydrogen gas, and introduce it into the centre of the globe.
The rarefied and vitiated air will ascend through the aperture
of the globe, and a constant supply of fresh air will be fur¬
nished from beneath. By this combustion, a quantity of water
will be generated, which will be condensed on the inner sur¬
face of the vessel.
III. A simple and ingenious apparatus, less costly than any
other, intended for the purpose of exhibiting the composition
of water, is made by Mr. Cuthbertson of London. It is de¬
scribed and figured in Nicholson’s Journal, 4 to. ii. 235; or in
the Philosophical Magazine, ii. 317 *; and also in plate iv. of
this work, figs. 33 and 34.
In using this apparatus, however, instead of two glass re¬
ceivers for the oxygen and hydrogen gases, standing inverted
in a trough of water, I employ a couple of gazometers ; and
with this alteration, the experiment is more easily managed.,
* In the same volume of the Philosophical Magazine, an interesting ac¬
count may be consulted of the principal experiments on the composition of
water, accompanied by neat and perspicuous engravings of the apparatus
employed in them.
168
WATER?
CHAP. VI
as well as more striking. The apparatus, thus modified, con¬
sists of a large glass receiver or bottle a (pi. iv. fig. 34), with
an opening at the bottom, into which is cemented a piece of
brass, perforated with two holes. This brass piece is repre¬
sented of a larger size in fig. 33 ; the aperture a conveying the
oxygen gas, and b the hydrogen. Before commencing the
experiment, the cock e, fig. 34, is screwed, by means of a
collar-joint*, to the cock b of the gazometer, fig 35, contain¬
ing oxygen gas ; and to the cock d9 by the same means, is
affixed another gazometer, filled with hydrogen gas.
When it is intended to ascertain, accurately, the propor¬
tions of gases consumed and of water generated, the receiver
a, previously weighed, is first exhausted by an air-pump, with
which it may be connected by the female screw at e. The
quantity of common air left in the receiver may be determined,
by enclosing a gauge wdthin it. If the additional expense be
not deemed an objection, it is adviseable, that after exhausting
the receiver, oxygen gas should be admitted : its contents be
exhausted a second time : and again renewed by fresh oxygen
from the gazometer, the quantity of which may be observed
by the graduated scale. The receiver being thus filled with
oxygen gas, and accurately closed by a cock at c, a succession
of sparks is to be passed, from the prime conductor of an
electrical machine, between the platina knob of the bent wire
wdthin the receiver, and the point of the brass cone. While
the sparks are transmitted, the cock d is to be opened. A
stream of hydrogen gas wdll immediately issue from the aper¬
ture at the point of the cone, and will be inflamed by the elec¬
tric spark, as represented fig. 33. The cock e is now' to be
opened, and the size of the flame of hydrogen gas moderated
by partly shutting the cock d. As the volume of hydrogen
gas consumed is double that of the oxygen; and the pipe,
which transmits it, is of less diameter than that conveying the
latter, about twdee the pressure is required to expel the hydro¬
gen. This is given, by lessening, in that proportion, the
weight of the counterpoises (ee9 fig. 35) of the gazometer con¬
taining hydrogen.
* See pi. v. fig. 47 ; and the corresponding description of the structure of
this joint, in the explanation of the plates at the end of the work.
SECT. I.
SYNTHESIS OF WATER.
169
During the combustion, the moveable vessel c, fig. 65, of
each gazometer descends: and, by observing the graduated
scales, it will be seen that the hydrogen vessel falls twice as
quick as that which holds the oxygen gas. It is necessarv to
keep the receiver a cool by means of wet cloths : and, when
this is done, the water, which is produced, will form into
drops on the inside of the receiver, and collect at the bottom.
At the conclusion of the experiment, the receiver is to be again
weighed, and the increase noted. The quantity of gases con¬
sumed is to be observed, and their actual weight computed,
by means of the table given in the Appendix. It will be found,
that the weight of water produced is very nearly equal to that
of the tw*o gases expended: that is to say, for every hundred
grains of water generated in the receiver, 88.3 grains of
oxygen gas, and 11.7 grains of hydrogen gas (equal by mea¬
sure to about 250 cubic inches of the former, and 500 of the
latter), will have disappeared from the gazometers.
Of the Proportion of the Elements of Water.
The precise determination of the proportions of oxygen
and hydrogen in water, is a problem of great importance, not
only on account of the fact itself, but of its influence on the
general theory of chemistry. The results of almost all the
i earliest experiments tended to prove, that water is a compound
of 85 parts by weight of oxygen, and 15 of hydrogen. These
numbers were afterwards corrected by Fourcroy, &c. to 85.7
of oxvgen, and 14.3 of hvdrogen ; and in 1805 it was shown,
by Humboldt and Gay Lussac, that the quantity of aqueous
vapour, which gases always contain, being subtracted, it is a
nearer approximation to truth to state the proportions at 87.4
and 12.6. It is admitted, on all hands, that water is formed
by the union of two volumes of hvdrogen gas, and one volume
ot oxygen gas. The greatest deviation from those numbers
that has ever been contended for, is that 100 measures of
oxygen gas combine with 197 of hydrogen. A difference,
however, so difficult to ascertain, on account of its minute¬
ness, maybe neglected: and it may be safely assumed, that
the general statement of one volume of oxygen to two of hy¬
drogen is correct.
170
WATER.
CHAP. VI.
In determining the proportion of the elements of water,
every thing will depend, therefore, on the precision with
which the specific gravities of oxygen and hydrogen gases are
ascertained. Taking the results of Biot and Arago as ac¬
curate (viz. 1.10359 for oxygen gas, and 0.07321 for hydro¬
gen gas), the proportion of the elements of water must
be as those numbers; and 100 grains must be composed
of
Oxygen . . . . 88.286
Hydrogen . 1 1.714?
100.
These proportions scarcely differ from those determined by
Berzelius (SI An. Ch. 25), viz.
Oxygen - 88.246 . . . .750.77 _ 100
Hydrogen . .11.754 . . ..100 . 13.33
100. 850.77 113.33
If then we admit, with Mr. Dalton, that water is com¬
pounded of an atom of oxygen united with an atom of hy¬
drogen, the relative weights of these atoms will be the same
as the relative weights of oxygen and hydrogen, ascertained
to form water, viz. for oxygen very nearly 7.5, and for hy¬
drogen 1. Or if, with Dr. Wollaston and others, we denote
the atom of oxygen by 1 0, the atom of hydrogen will bear
to 10 the same ratio that 1 bears to 7.5, viz. it will be denoted
by l .327. It should be observed, that Mr. Dalton has de¬
duced the relative weight of the atom of oxygen to be to that
of hydrogen as 7 to 1 But this determination is founded on
the results of Humboldt and Gay Lussac, and not on the
more recent, and probably more correct ones of Biot and
Arago.
It must be allowed, however, to be possible, though it is a
much less probable view of the subject, that water may be a
compound of two atoms of hydrogen with one of oxygen,
which would double the weight of the atom of oxygen, and
* New System, p. 275.
SECT. II.
ANALYSIS OF WATER.
171
make it 15, the number assumed by Sir H. Davy. But
hitherto we have no evidence that oxygen and hydrogen
unite in any other proportion, than that constituting water ;
for whatever excess we employ of the one gas, or of the other,
the surplus invariably remains without alteration. Now it
admits of being proved to be consistent with mechanical prin¬
ciples, that the most energetic combination of any two ele¬
ments is that, in which they are united particle to particle.
Until, therefore, the contrary can be established, we may
assume, with Mr. Dalton, that water is a binary compound
of 1 atom of oxygen, and 1 atom of hydrogen : and, adding
the weights of these atoms together (7.5 + 1), an atom of
water will weigh 8.5. The same proportions, expressed by
different numbers, as proposed by Dr. Wollaston, will make
the relative weight of an atom of water 10.000 -f 1.327
= 11.327; the only difference in this way of stating the fact,
being, that oxygen, instead of hydrogen, is expressed by the
decimal unit.
SECTION II.
Analysis, or Decomposition , of Water .
The analytic experiments on water are of two kinds :
1st, Such as present us with one of its ingredients only, in
a separate and distinct form ; 2dly, Such as present us with
its two component principles, the hydrogen and oxygen,
mixed together in the state of gas.
I. Of the first kind are the following :
1. Procure a gun-barrel, the breech of which has been
removed, so as to form a tube open at each end. Fill this
with iron wire, coiled up in a spiral form. To one end of
the barrel adapt a small glass retort, partly filled with water,
and to the other a bent glass tube, the open end of which
terminates under the shelf of the pneumatic cistern. Let
the barrel be placed horizontally (or rather with that end, to
which the retort is fixed, a little elevated) in a furnace, which
has two openings in its body opposite to each other. (PI. iv»
172
WATER.
CHAP. VI.
fig. 40.) Light a fire in the furnace; and, when the gun-
barrel has become red-hot, apply a lamp under the retort.
The steam of the water will pass over the red-hot iron, and
will be decomposed. Its oxygen will unite with the iron ; and
its hydrogen will be obtained in the form of a gas. This is
the readiest and cheapest mode of procuring hydrogen gas,
when wanted in considerable quantity.
2. The same experiment may be repeated ; substituting an
earthen tube for a gun-barrel, and weighing the iron wire
accurately, both before and after the experiment. The iron
will be found to have gained weight very considerably ; and,
if attention be paid to the weight of the water that escapes
decomposition, by an addition to the apparatus (fig. 40, <?),
and to the weight of the hydrogen gas obtained, it will be
found, that the weight gained by the iron, added to that of
the hydrogen gas, will make up exactly the weight of the
water that lias disappeared. From experiments of this kind,
conducted with the utmost attention to accuracy, as well as
from synthetic experiments, Lavoisier inferred, that water is
compounded of 85 per cent . oxygen, and 15 hydrogen, by
weight, very nearly. But as hydrogen gas is eleven times
lighter than common air, the proportion of gases, by volume,
required to form water, is about two of hydrogen to one of
oxygen gas. By the decomposition of every hundred grains ;
of water, therefore, the iron employed gains 85 grains, and l
becomes oxidized; and 15 grains (equal to about 500 cubical
inches) of hydrogen gas are obtained.
3. Water may be decomposed, in a similar apparatus, over
charcoal instead of iron. The results, however, are different
in this case, as will appear from a subsequent section.
4. Another mode of effecting the decomposition of water
yet remains to be mentioned, in which not the hydrogen, but :
the oxygen, is obtained in a gaseous state. This is by the
action of living vegetables ; either entire, or by means of their
leaves only. Fill a clear glass globe with water, and put into
it a number of green leaves, from almost any tree or plant.
A sprig or two of mint will answer the purpose perfectly well.
Invent the glass, or place it, with its mouth downwards, in * tj
SECT. ir.
ANALYSIS OF WATER.
173
vessel of water. Expose the whole apparatus to the direct
light of the sun, which will then fall on the leaves surrounded
by water. Bubbles of air will soon begin to form on the
leaves, and will increase in size, till at last they rise to the
top of the vessel. This process may be carried on as long as
the vegetable continues healthy ; and the gas, when examined*
will prove to be oxygen gas, nearly pure. In this experi¬
ment, the hydrogen combines with the plant, to the nourish¬
ment and support of which it contributes, while the oxygen is
set at liberty.
II. The processes, by which the elementary parts of water
are separated from each other, and are both obtained in an
aeriform state, as a mixture of hydrogen and oxygen gases,
are dependent on the agency of electricity.
1. The first of these experiments requires for its perform¬
ance the aid of a powerful electrical machine. This fact was
the discovery of a society of Dutch chemists ; and the prin¬
cipal circumstance, in the experiment, is the transmission of
electrical shocks, through a confined portion of water. The
apparatus employed, in this experiment of Messrs. Dieman
and Van Troostwyk, is a glass tube, about one 8th of an inch
diameter, and 12 inches long, one of the ends of which is
sealed hermetically, a gold wire being inserted at this end,
and projecting about an inch and a half within the tube.
About the distance of five 8ths of an inch from the extremity
of this, another wrire is to be fixed, which may extend to the
open end of the tube. The tube is next to be filled with dis¬
tilled water, and to be placed inverted in a vessel of the same.
When thus disposed, electrical shocks are to be passed be¬
tween the two ends of the wire, through the water; and, if
these shocks be sufficiently strong, bubbles of air will be
formed at each explosion, and will ascend till the upper part
of the wire is uncovered by the water. As soon as this is
effected, the next shock that is passed will set fire to the mixed
gases, and the water will rise again in the tube, a very small
quantity of gas remaining. Now, as hydrogen and oxygen
gases, in a state of admixture, are the only ones that are
capable of being inflamed by the electric shock ; and as there
is nothing in the tube, beside water, that can afford them in
6
17*
WATER.
CHAP. VI.
this experiment, we may safely infer, that the evolved hy¬
drogen and oxygen gases arise from decomposed water.
2. An improved apparatus, exhibiting the same experiment,
with less trouble to the operator, has been invented by Mr.
Cuthbertson, and may be seen described and figured in Dr.
Pearson’s paper in the Philosophical Transactions for 1797,
or in Nicholson’s Journal, vols. i. and ii. 4to.
3. The decomposition of water by galvanic electricity is a
process singularly adapted to demonstrate the fact in a simple
and elegant manner. The manner of conducting it, as well
as the results, will be fully explained, when we come to treat
of the general principles of electro-chemical science.
SECTION III.
Properties and Effects of Water *.
I. Water contains air . — This may be shown by placing a
glass vessel of water under the receiver of an air-pump.
During the exhaustion of the receiver, bubbles of air will be
seen to ascend very plentifully. Much air escapes also from
water, during boiling, and may be collected by a proper
apparatus. The same fact may also be exhibited, by filling a
barometer tube, about 32 inches long, sealed at one end,
with quicksilver, except about four inches, and the remainder
with water. On inverting the open end of the tube in quick¬
silver, bubbles of air will be seen, in a short time, to rise
from the water.
The kind of gas, extricated from the water of a spring at
a considerable distance from the surface, I have made the ob¬
ject of experiment f. From 100 cubic inches of the water,
or about 3-1- wine pints, 4.76 cubic inches of gas were sepa¬
rated, of which 3.38 were carbonic acid gas, and 1.38 air of
the same standard as that of the atmosphere.
* W henever in the course of this work, water is mentioned as an agent in
any chemical operation, pure distilled water is to be understood,
f Philosophical Transactions, 1803.
SECT. III.
PROPERTIES OF WATER.
175
It is probable that the proportion of gaseous contents dif¬
fers in the water of different springs, for Mr. Dalton states
the average of his experiments to be about 2 inches from
100 of water, and that the air expelled, after losing 5 or 10
per cent, of carbonic acid by the action of lime-water, consisted
of 38 per cent, oxygen and 62 nitrogen *.
Every gas is absorbed by water, deprived of all or the great¬
est part of its air by long boiling. The quantity, however,
- which water is capable of absorbing, varies considerably with
[ respect to the different gases. Those, of which only a small
[ proportion is absorbed, require violent and long continued
s agitation in contact with water. The following table has
[ been drawn up by Mr. Dalton from the combined results of
I his own experiments and mine.
Water absorbs, at the mean pressure and temperature of
\ the atmosphere,
Of carbonic acid gas . . its own bulk.
sulphureted hydrogen . . . do.
nitrous oxide . . do.
olefiant gas .
oxygen gas. ......
nitrous gas .7 .
carbureted hydrogen
carbonic oxide .
azotic gas .........
hydrogen gas .
The accuracy of these results has been called in question by
a Saussure f, who, from a series of experiments of his own, has
deduced the numbers expressed in the second column of the
following Table.
Gases. 100 volumes of water 100 volumes of water
absorb (Dalton and Henry) absorb (Saussure)
Sulphureted hydrogen .... 100 ............ 253
Carbonic acid. . . . 100 ............ 106
Nitrous oxide . . 100 ............ 76
Olefiant gas . 12.5 . . 15.3
* New System, p. 271. f Thomson's Annals, vi. 340.
T*
i
TT*
do.
do.
i
TT*
do.
do.
176
WATER.
CHAP. VI,
Gases. 100 volumes of water 100 volumes of water
absorb (Dalton and Henry) absorb (Saussure)
Oxygen . . 3.7 6.5
Carbonic oxide . . 1.56 . 6.2
Azotic . 1.56 . 4.1
Hydrogen . 1.56 . 4.6
Absolutely pure water (not merely freed from air by boil¬
ing) according to recent experiments of Mr. Dalton, takes up
2J per cent, of its bulk of azotic gas, and two per cent . of hy¬
drogen. In the other gases, he is disposed to abide by his
original numbers, and to consider those of Saussure as much
greater than the truth
II. Water is contained in the air of the atmosphere , even
during the driest weather . — Expose to the air, in a shallow
vessel, a little sub-carbonate of potash or common salt of tar¬
tar. In a few days it will have become moist, or deliquiated .
On the same principle, water exposed to the air, in a shallow
vessel, disappears, being dissolved by the atmosphere. Saus¬
sure states the quantity of water in a cubic foot of air, charged
with moisture at 65° of Fahrenheit, to be 11 grains. The
quantity of water, that may be extracted from 100 cubical
inches of air, at 57° Fahrenheit, is 0.35 of a grain; but, ac¬
cording to Clemont and Desormes, at 54° Fahrenheit, only
0.236 of a grain can be detached by exposure to muriate of
lime. The experiments, both of these chemists and of Mr.
Dalton, concur in proving that at the same temperature, equal
bulks of different gases give up the same quantity of water to
deliquescent salts. The portion of humidity, which they thus
abandon, has been called hygrometric water. Whether they
contain a still farther quantity in a state of more intimate
union and not separable by deliquescent substances, is still
undetermined.
III. Several bodies absorb water from the atmosphere,
which can scarcely be supposed to have an affinity for it, and
again give it up, on the application of a gentle heat. Such
are almost all substances in the state of powder ; porous
paper ; soils which have been artifically dried ; parched oat-
* Thomson’s Annals, vii, 215.
SECT. III.
PROPERTIES OF WATER.
177
i
rj
i
>j
i
• !
t
i
\
*1
[
r
i
>i
5
f
t\
!
£
J!
ii
f
)
[
>
5
Ej
>
meal ; and even the filings of metals. Some powders retain
the moisture they have absorbed, till a considerable heat is
applied *. The nature of this combination is not exactly un¬
derstood.
There are two different theories of the state, in which water
exists in the atmosphere and in other gases. By most writers,
it has been considered as united to air by chemical affinity ;
and, when abstracted by other bodies, (as sulphuric acid, lime,
and the whole class of deliquescent salts) the effect has been
ascribed to the superior affinity of those bodies for water. Mr.
Dalton first took a different view of the subject, viz. that the
vapour of water, mixed with air and other gases, differs in no
respect from pure steam, and is subject to the same laws. It
constitutes, indeed, in his opinion, a distinct and independent
atmosphere, the elastic force of which forms, at different tem¬
peratures, different proportions of the elastic force of the
whole; for example, at the temperature of 65° Fahrenheit, it
gives to air of its elasticity. This theory appears to have
much more probability, than that which explains the pheno¬
mena by chemical affinity ; and it is supported, especially, by
the absorption of caloric, which is ascertained to be of the
same amount in spontaneous as in forced evaporation.
Instruments for measuring the degree of moisture of the air
are called hygrometers . They consist, for the most part, of
some substance, such as a human hair or a fine slip of whale¬
bone, which is elongated by a moist atmosphere, and short¬
ened by a dry one. The extreme points are attained by
placing it, first in air artificially dried, and then in air ren¬
dered as humid as possible. The degree of expansion or con¬
traction is rendered more sensible by connecting it with an
axis, which moves a circular index, like the finger of a clock.
Mr. Leslie, by a slight modification of his differential ther¬
mometer, makes it serve the purpose of an hygrometer ; for if
one of the balls be covered with silk, and then moistened with
water, the rate of evaporation will be shown by the degree of
cold produced, as indicated by the descent of the liquid in the
opposite leg of the instrument. The drier the air, the quicker
* Berzelius, 79 An. Cbim. 118.
VOL* I
N
m
WATER.
chap, vr*
will be the evaporation, and the greater the effect in moving
the liquid within the instrument.
A new kind of hygrometer has lately been constructed by
Mr. Wilson, of Dublin. It consists of the urinary bladder of
a rat or other small animal, into which a thermometer tube is
inserted, the bladder being afterwards filled with mercury,
and tied firmly over the tube with a silk thread. The point
of extreme moisture is taken by immersing the bladder in wa¬
ter of the temperature of 60° Fahrenheit, and that of extreme
dryness, by enclosing the bulb in air, dried by contact with
concentrated sulphuric acid. The interval is divided into 100
equal parts, 0 being placed at the point of extreme dryness,
and 100 at that of extreme moisture. Some correction of the
results obtained with this instrument is necessary, on account
of the effects of changes of temperature on the bulk of the
mercury
IV. Water enters into combination with various solid bodies ,
and entirely loses its fluid form. In many instances, it unites
only in a definite proportion ; and it is retained by so power¬
ful an affinity, as not to be separated by a very high tempera¬
ture. Such compounds are termed hydrates , or, as Gay Lussac
has proposed, hydroxures f . The pure alkalies, potash, and
soda, retain, for example, even after fusion, about j- their
weight of water, which can only be separated by some body
having a stronger affinity for the alkali. In all hydrates, at
least one atom of water must be present, or it must be con¬
tained in them in such quantity, as to bear the proportion of
at least 8.5 to the weight of the atom with which it is united.
If, for example, the weight of the atom of potash be 48, as Sir
H. Davy supposes, we cannot have a true chemical compound
of water and potash, in which the former bears to the latter
a less proportion than that of 8.5 to 48. And if, in any in¬
stance, water is obtained from a compound in a proportion
less than that of the weight of the atom of water, to the weight
of the atom of the body with which it is associated, we may
take for granted that it is held mechanically and accidentally,
* Thomson's Annals, ix. 313.
f Ann, de Chim. et Phys. i. 170*
SECT. III.
PROPERTIES OF WATER*
and not as a true chemical constituent. Such appears to be
the nature of the union of water with certain neutral salts
(common salt for example) which contain only 1 or 2 per
cent of their weight of water.
V. Water dissolves a great variety of solid bodies.— The sub-
stances, on which it exerts this effect, are said to be soluble in
water ; and there are various degrees of solubility. See chap, i.
and the table in the Appendix.
VI. During the solution of bodies in water , a change of tem¬
perature ensues.— In most instances, an absorption of caloric
(in other words, a production of cold) is attendant on solution,
as in the examples given in chap. iii. sect. 2. But, in other
cases, caloric is evolved, or heat is produced. Thus, common
i salt of tartar, during solution in water, raises the temperature
of its solvent; and caustic potash, in a state of dryness, does
the same still more remarkably. Both carbonated and pure
potash, however, when crystallized, observe the usual law, and
; absorb caloric during solution. Now as their difference, in
the crystallized and uncrystallized state, depends chiefly on
i their containing in the former, but not in the latter, water
chemically combined, we may infer, that the cold, produced
h during the solution of salts, is occasioned by the conversion of
the water, which exists in these bodies, from a solid to a li¬
quid form. Some doubt, it must be acknowledged, is thrown
on this conclusion by the observation of Gay Lussac, that a
saturated solution of nitrate of ammonia mixed with water of
the same temperature is cooled 8 or 9 degrees *.
VII. During the solution of salts in water , a quantity of air is
disengaged . — This air was partly contained mechanically in the
salt, and partly in the water. That it does not arise entirely
from the former source, is proved by varying the experiment in
the following manner. Let an ounce or two of sulphate of soda
be put into a vial, and on this let as much water be poured as
will completely fill the bottle. The air contained in the pores
of the salt will be thus disengaged ; but only a small portion
of the salt will be dissolved, agreeably to the principle laid
down, chap. ii. 7. Let the vial be shaken, and the whole of
* An de Chim, et Phys, i. 21$.
N 2
ISO
WATER.
CHAP. VI,
the salt will disappear ; a fresh portion of air being liberated
during its solution.
VIII. During the solution of bodies, the bulk of ivater changes .
— Take a glass globe, furnished with a long narrow neck
(commonly termed a matrass, see fig. 4), and put into it an
ounce or two of sulphate of soda. Then, add as much water
as will fill the globe, and about three 4ths of the neck. This
should be done with as little agitation as possible, in order
that the salt may not dissolve, till required. Mark, by tying
a little thread, or by a scratch with a file, the line where the
water stands ; and then agitate the matrass. The salt will
dissolve ; air will be set at liberty ; and, during the solution?
the water will sink considerably below its level. The contrac¬
tion of bulk is owing to the diminution of temperature; and?
when the water has regained its former temperature, it will
also be found, that its bulk is increased by the addition of salt.
The late Bishop Watson observed, that water exhibits a mani¬
fest augmentation of bulk, by dissolving only the two thou¬
sandth part of its weight of salt ; a fact sufficiently decisive
against that theory, which supposes pores in water capable of
receiving saline bodies without an augmentation of volume.
IX. Water has its solvent power increased , by diminishing the
pressure of the atmosphere . — Into a Florence flask, put half
a pound of sulphate of soda ; pour on it barely a pint of water?
and apply heat so as to boil the wTater. The whole of the
salt will be dissolved. Boil the solution for several minutes
pretty strongly, so as to drive out the air ; and cork the bottle
tightly, immediately on its removal from the fire. To pre¬
vent more completely the admission of air, tie the cork over
with bladder. As the vessel cools, an imperfect vacuum will
be formed over the solution; for the steam which arises during
the ebullition expels the air? and takes its place. The steam
is condensed again, when the vessel cools. The solution?
when perfectly cold, may be shaken wdthout any effect en- .
suing, so long as the vessel is kept closely stopped ; but, on
removing the cork and shaking the vessel, the solution will
immediately congeal, and heat will be produced. This ex¬
periment, besides the principle which it is peculiarly intended
to illustrate, exemplifies also the general rule laid down,,
SECT. III.
PROPERTIES OF WATER.
181
chap. iii. sect. 2. vi. viz. that caloric is always evolved, du¬
ring the transition of bodies from a fluid to a solid state;
and it furnishes a fact exactly the reverse of that in which
cold is produced, or caloric absorbed, during the solution of
■ salts. It is proper, however, to remark that the observations
of Dr. Coxe, of Philadelphia *, have th rown some doubt
over the cause of these phen omena, which appears to require
farther investigation. From his experiments, the exclusion
of air does not seem to be absolutely necessary ; for saline so¬
lutions continued fluid, if perfectly at rest, though freely ex¬
posed to the atmosphere, but immediately became solid when
3 shaken *. The efficacy of mechanical disturbance in pro¬
moting saline crystallization, under circumstances where it
has been ascribed to the renewed contact of air with the
ii surface of the solution, is illustrated also by some experiments
; of Dr. Uref.
X. It is unnecessary to add any thing to what has been
r already said in a former section, respecting the combination
o of caloric with water constituting steam ; or to the history of
[j the phenomena attending its conversion into ice; except that,
1: during the latter change, its bulk is enlarged in the propor-
i; lion of nine to eight, and that, in consequence of this exp an¬
il sion, water, during congelation, is capable of bursting the
ii strongest iron vessels; and becomes specifically lighter. Hence,
3 ice swims always on the surface of the water.
It is remarkable, that this enlargement of the bulk of water
x begins long before its temperature has descended to the freez-
l ing point, viz. at about 40° Fahrenheit. Let a thermometer
bulb, and part of its tube, having a wide bore, be Ailed with
water, tinged with a little litmus, which may be introduced
by the same means as those already directed for filling with
3 j quicksilver. Immerse the thermometer in water of the temper¬
ature of 40° ; and, when the included water may be supposed to
have attained the same degree of heat, remove the instrument
successively into water of the temperature of 36° and 32°. At
f each immersion, the water will rise in the tube. Bring its
tj temperature again , to 40°, and it will descend to the same
* Thomson’s Annals, vi. 101. t Journal of Science, &c. v. 106.
182
WATER.
CHAP. VI.
point as before. Place it in water of 50°, and it will again be
expanded. Precisely similar effects, therefore, appear to result,
in these experiments, from two opposite causes ; for the bulk
of water is alike increased by reducing or raising its tempera¬
ture. It is contended, however, by Mr. Dalton, that, in the
apparent expansion by a lower temperature, there is a decep¬
tion, arising from the contraction of the glass, which must
lessen the capacity of the bulb, and force the water up the
stem. The question is not yet decided ; and is still contested
by Mr. Dalton against the experiments of Count Rumford
and of Dr. Hope. The first mentioned philosopher now con¬
tends, that water is of the greatest density at 36° of Fahren¬
heit, or 4° above its freezing point, and M. Biot infers that
the true maximum of density is at 38.16 of Fahr.*
Thomson's Annals, ix. 434.
IBS
CHAPTER VII.
ON THE CHEMICAL AGENCIES OF COMMON AND
GALVANIC ELECTRICITY.
That branch of natural science which comprehends the
phenomena of Galvanism, and the general principles under
which they are arranged, is only of recent origin. It was not
till the year 1791, that Galvani, an Italian philosopher, being
engaged in a course of experiments on animal irritability,
observed accidentally the contractions, which are excited in
? tile limbs of frogs, by applying a conductor of electricity be¬
tween a nerve and a muscle. The theory, which he framed
to account for this phenomenon, was, that the different parts
of an animal are in opposite states of electricity, and that the
effect of the metal is merely to restore the equilibrium. The
si analogy, however, was afterwards shown to be without foun¬
dation, by Volta, who excited similar contractions by making
a connection between two parts of a nerve, between two mus-
] eles, or between two parts of the same muscle ; but to produce
the effect, two different metals were found to be essential.
Hence he was led to infer that, by the contact of different
metals, a small quantity of electricity is excited ; and to the
agency of this electricity, first upon the nerves, and through
their mediation on the muscles, he ascribed the phenomena
in question.
Several years elapsed, during which the action of galvanic
electricity on the animal body, and the discussion of its cause,
occupied the attention of philosophers. Early in 1800, the
subject took a new turn, in consequence of the discovery by
Signor Volta of the Galvanic Pile * ; a discovery which has
furnished us with new and important instruments of analysis,
capable, if any such there are, of leading to a knowledge of
the true elements of bodies. From this period, discoveries
have multiplied with a rapidity, and to an extent, which sur-
# Philosophical Transactions, 1800 ; or Philosophical Magazine, vii. 289.
184
ELECTRO-CHEMISTRY*
CHAP. Vile,
pass anything before known in the history of science; and the
facts are now become so numerous, that an arrangement and
classification of them seem to be preferable to an historical
detail in the order of time. The method, which appears to
me best calculated to give a distinct view of the subject, is to
describe,
I. The construction of galvanic apparatus, and the circum¬
stances essential to the excitement of this modification of elec¬
tricity :
II. The facts, which establish its identity with the electri¬
city excited by ordinary processes :
III. The agency of the electric or galvanic fluid in pro¬
ducing chemical changes :
IV. The theory, by which these changes, in the present
state of our knowledge, are best explained : And
V. The hypotheses, which have been framed to account for
the origin of the electricity, excited by galvanic arrangements*
SECTION I.
Of the construction of Galvanic Arrangements .
For the excitation of ordinary electricity, it is well known
that a class of substances are required, called electrics , by the
friction of which the electric fluid is accumulated, and from
which it may be collected by a different class of bodies termed
non-electrics or conductors . When friction, for example, is
applied to the glass cylinder or plate of an electrical machine,
that part of the glass, which is in contact with the rubber, at¬
tracts the electric fluid from it, as well as from all other con¬
ducting bodies, with which the rubber is connected. The
glass, regaining instantly its natural state, repels the electric
fluid, which is received by the prime conductor, placed for
that purpose. Ail then that is effected, by the action of the
machine, is a disturbance of the natural quantity of electricity
in bodies, or a transfer of it from some to others, in conse¬
quence of which, while the latter acquire a redundance, the
former become proportionally deficient in their quantity of
electricity.
SECT. I.
ELECTRO-CHEMISTRY*
185
The conditions necessary to the excitement of galvanic elec¬
tricity are altogether different ; for the class of bodies, termed
electrics, have now no longer any share in the phenomena. All
that is required is the simple contact of different conducting
bodies with each other ; and it has even been found by Des-
saignes that two discs of the same metal, heated to different
temperatures, give sufficient electricity to excite contractions
in the legs of a frog, prepared for the purpose. Conductors
of electricity have been divided into perfect and imperfect , the
former comprehending the metals, plumbago and charcoal,
the mineral acids, and saline solutions ; the latter, or imperfect,
including water, alcohol and ether, sulphur, oils, resins, me¬
tallic oxides, and compounds of chlorine.
The least complicated galvanic arrangement is termed a
simple galvanic circle. It consists of three conductors,
two of which must be of the one class, and one of the other
class. In the following Tables, constructed by Sir H. Davy,
some different simple circles are arranged in the order of their
powers, the most energetic occupying the highest place.
Table of some Electrical Arrangements , which by combination
form Voltaic Batteries , composed of two Conductors and one
imperfect Conductor.
Zinc,
Iron,
Each of these is the po-
Solutions of nitric acid,
Tin,
sitive pole to all the
of muriatic acid,
Lead,
metals below it, and
of sulphuric acid,
Copper,
negative with respect
of sal ammoniac,
Silver,
to the metals above it
of nitre,
Gold,
in the column.
of other neutral
Platina,
Charcoal.
salts.
Table of some Electrical Arrangements , consisting of one Con
ductor and imperfect Conductors .
Copper,
Silver,
Nitric acid,
Solution of sulphur and potash,
Lead,
Sulphuric acid,
of potash,
Tin,
Muriatic acid.
of soda.
Zinc,
Any solutions
Other Metals,
Charcoal.
containing acid.
ELECTRO-CHEMISTRY.
CHAP. VI r .
In explanation of these Tables, Sir H. Davy observes, that
in all cases when the fluid menstrua afford oxygen, those
metals, which have the strongest attraction for oxygen, are
those which form the positive pole. But when the fluid men¬
strua afford sulphur to the metals, the metal which, under
the existing circumstances, has the strongest attraction for
sulphur, determines the positive pole. Thus, in a series of
copper and iron plates, introduced into a porcelain trough,
the cells of which are filled with water or with acid solutions,
the iron is positive and the copper negative; but when the
cells are filled with solution of sulphuret of potash, the copper
is positive and the iron negative. When one metal only is
concerned, the surface opposite the acid is negative, and that
in contact with solution of alkali and sulphur, or of alkali, is
negative *.
The powers of simple galvanic circles are but feeble ; but
they may be made sufficiently apparent by the following ex¬
periments.
1. When a piece of zinc is laid upon the tongue, and a
piece of silver under it, no sensation is excited, so long as the
metals are kept apart ; but, on bringing them into contact, a
metallic taste is distinctly perceived. In this case we have an
example of the arrangement of two perfect conductors (the
metals) with one imperfect one (the tongue, or rather the
fluids which it contains). The metallic taste arises, in all
probability, from the excitement of a small quantity of elec¬
tricity by the contact of the metals, and its action on the
nerves of the tongue.
2. A piece of zinc, immersed under writer which is freely
exposed to the atmosphere, oxidizes very slowly; but when
placed in the same situation, in contact with a piece of silver,
its oxidation is much more rapid. By immersing iron and
silver (also in contact with each other) under diluted muriatic
acid, the action of the acid upon the iron is considerably
increased; and hydrogen gas is evolved from the water, not
only where it is in contact with the iron, but where it touches
the silver. These facts explain, why, in the sheathing of
* E1. of Chem. Phil. p. 148.
SECT. r.
ELECTRO-CHEMISTRY.
187
ships, it is necessary to use bolts of the same metal which
forms the plates ; for if two different metals be employed, they
both oxidate or rust very speedily, in consequence of their
forming, with the water of the ocean, a simple galvanic circle.
Of compound Galvanic Circles or Batteries,
Galvanic batteries are formed by multiplying those arrange¬
ments, which compose simple circles. Thus if plates of zinc
and of silver, and pieces of woollen cloth of the same size as
the plates and moistened with water, be piled upon each other
(fig. 77) pi. ix), in the order of zinc, silver, doth ; silver, zinc,
cloth ; and so on, for twenty or more repetitions, we obtain
a galvanic battery termed, from its discoverer, the Pile of
Volta. The power of such a combination is sufficient to give
a smart shock, as may be felt by grasping in the hands, which
should be previously moistened, two metallic rods, and touch¬
ing with these the upper and lower extremities of the pile.
The shock may be renewed at pleasure; until, after a few
hours, the activity of the pile begins to abate, and finally
ceases altogether.
The metals, composing a galvanic battery, may be more
conveniently arranged in the form of a trough, a happy inven¬
tion of Mr. Cruickshank. In a long and narrow wooden
trough, made of baked wood, grooves are cut, opposite to
and at the distance of between y and -f- of an inch from each
other ; and into these are let down, and secured by cement,
square plates of zinc and copper, previously united together
by soldering. (See figs. 37 and 78.) The space, therefore,
between each pair of plates, forms a cell for the purpose of
containing the liquid, by which the combination is to be made
active. The advantage of this contrivance, over the pile, is
partly that it is much more easily put in order ; but, besides
this, it is a more efficient instrument. When constructed in
the way which has been described, it affords an example of a
galvanic combination of the first kind , formed by two perfect
and one imperfect conductor. But it admits of being modi¬
fied, by cementing, into the grooves, plates of one metal only,
and filling the cells, alternately, with two different liquids, as
diluted nitric acid and solution of sulphuret of potash. In
ELECTRO-CHEMISTRY.
CHAP, vxr.
this case, we have a battery of the second order , formed by the
repetition of one perfect and two imperfect conductors. For
all purposes of experiment, the first kind of arrangement is
universally preferred.
Another modification of the apparatus, which may be called
the Chain of Cups , was proposed by Volta at the same time
that he communicated his invention of the Pile; and, from
the recent experiments of Mr. Children *, it appears to be a
very useful and powerful one. It consists of a row of glasses
(see fig. 75), such as wine glasses or small tumblers, for the
purpose of containing any fluid that may be selected. Into
each of these glasses is plunged a plate of zinc and another of
copper, each not less than an inch square, which are not to
touch each other. The plates of different cups are connected
by metallic wires or arcs, in such a manner that the zinc of
the first cup communicates with the copper of the second;
the zinc of the second with the copper of the third ; and so
on through the whole row. The shock is felt on dipping the
fingers of one hand into the fluid of the first cup, and those
of the other hand into the last of the series. The superiority
of this arrangement consists in both surfaces of each metallic
plate being exposed to the action of the liquid ; whereas, by
soldering the plates together, one of the surfaces of each is
protected from the liquid, and contributes nothing to the
effect. The common trough has lately been made to com¬
bine this advantage, by dividing it into cells, not by plates of
metal, but by partitions of glass. Into each of these cells
filled with the proper liquid, a plate of each metal is intro¬
duced, but not so as to touch each other. A communication
is then made, by a metallic arc, between the zinc plate of each
cell and the copper one of the next, precisely as in the chain
of cups. More lately the troughs themselves have been made
of earthen ware, and the partitions of the Same material ; the
apparatus being completed, in other respects, in the manner
already described. The plates, also, are now so suspended
that when not in use, they may all be lifted out of the cells at
once f. And it has been recently ascertained that the power
* Philosophical Transactions, 1309, page 32.
f See Pepys in Journal of Science, &c. i. 193.
SECT. I.
ELECTRO-CHEMISTRY®
1851
'
t
i
!
I
r
i
*»
;
i
I
of a battery is increased at least one half by placing in each
cell one zinc and two copper plates, so that each surface of
zinc may be opposed to a surface of copper #.
The size of the plates has been varied from one or two
inches to several feet. The large battery, described by Mr.
Children in the Philosophical Transactions for 1815, con-
sisted of plates each six feet by two feet eight inches, equal to
32 square feet ; and the cells were capable of containing about
945 gallons of liquid. For ordinary purposes, plates of two
inches square are sufficient; but for the decomposition of
several bodies, not less than 100 pairs of plates, each four
inches square, are required f. The enlargement of the size
of the troughs, so as to contain this number, would be ex¬
tremely inconvenient; and we may therefore combine the
power of several troughs, by uniting the zinc end of the one
with the copper end of the other, by the intervention of a
metallic wire, or by an arc of silver or zinc.
It may be sufficient to add, in general terms, that every
combination, which is capable of forming a simple galvanic
circle, may, by sufficient repetition, be made to compose a
battery. The combinations, also, which are most active in
simple circles, are observed to be most efficient in compound
ones. The foregoing tables of Sir H. Davy express, there¬
fore, the powers of compound as well as of simple arrange¬
ments.
To construct a battery of the first order , it is essential that
a fluid be employed, which exerts a chemical action upon one
of the metals. Pure water, entirely deprived of air, appears
to be inefficient. In general, indeed, the galvanic effect is,
within certain limits, proportional to the rapidity with which
the more oxidable metal is acted upon by the intervening
fluid. Spring water was found sufficient, in Mr. Children’s
immense battery, to produce the ignition of platina wire. The
fluid generally used is nitric acid, diluted with 20 or 30 times
CD */
* Phil. Trans. 1815.
f Some useful information respecting the number and size ol plates,
a adapted to different purposes, is given by Mr. Singer in Nicholson’s Jour¬
nal, xxiv. 174.
4
190
ELECTRO-CHEMISTRY*
CHAP. VII*
its weight of water. Mr. Children recommends a mixture of
three parts fuming nitrous acid, and one sulphuric, diluted
with thirty parts of water. Directions, also, respecting the
best kind and density of acids, for producing galvanic electri¬
city, are given by Mr. Singer. From his experiments it ap¬
pears, that acid of different densities is required for different
purposes. The best wire melting charge is formed with ten
gallons of water, five pounds of nitric acid, and half a pound
of muriatic acid.
The power of the apparatus has been found to be increased,
when insulated by non-conductors ; and when surrounded by
an atmosphere of oxygen gas; not sufficiently, however, to
make it necessary to resort to either of these expedients in
ordinary cases. Oxygen gas disappears in this process, when
carried on under a receiver ; and, after all the oxygen is ab¬
sorbed, the effect ceases, and is renewed by introducing a fresh
portion. A battery, also, which has ceased to be efficient,
has its activity renewed by emptying the ceils of their liquor,
and uncovering the plates. When the cells are filled with
diluted nitric acid, the apparatus continues active, even under
the exhausted receiver of an air-pump, or in an atmosphere
of carbonic acid or nitrogen gases. But if the cells be filled
with water only, all action is suspended, by placing it under
any of these circumstances. Hence it appears that the oxida¬
tion of one or both of the metals, composing the trough, is
essential to the excitement of galvanic electricity.
The electric column may be classed among galvanic arrange¬
ments. It was originally contrived by M. de Luc, who formed
it of discs of Dutch gilt paper, alternated with similar discs
of laminated zinc. These were piled on each other in a dry
state, and the instrument, instead of being soon exhausted,
like the pile with humid substances, was found to continue
active for some years *. A similar pile may be formed by
laying a mixture of very finely powdered zinc with common
glue and a little sugar, by means of a brush, on the back of
Dutch gilt paper; and, when dry, cutting it into discs, which
are to be piled on each other t. Zamboni of Verona has con-
* Nicholson’s Journal, vol. xxvi.
f Phil. Mag. xlvii. 265.
SECT. II.
ELECTRO-CHEMISTRY.
191
gtructed a pile of slips of silver paper, on the nnsilvered side
of which is spread a layer of black oxide of manganese and
honey. These papers are piled on each other to the number
of 2000 ; then covered externally with a coating of shell lac ;
and enclosed in a hollow brass cylinder. Two of these piles
are placed at the distance of four or five inches from each
other ; and between them is suspended on a pivot a light me¬
tallic needle, which is attracted alternately to the one pile
and the other, so that it moves between them like a pendulum.
This instrument has been applied to the measurement ol time,
by causing it to give motion to the pendulum of a clock
SECTION II.
On the mutual Relation of Electricity and Galvanism .
Is the influence, it may now be inquired, which is called
i into action in a way so different from that employed for the
s excitation of ordinary electricity, identical with it or of a dif-
| ferent kind ? This question will be decided by examining
| whether any of those phenomena, which are occasioned by
[;i the agency of the electric fluid, are produced also by that of
<s galvanism; and we shall find the following striking resem-
tl blances:
1. The sensation, produced by the galvanic shock, is ex-
d tremely similar to that which is excited by the discharge of a
] Leyden jar. Both influences, also, are propagated through a
i number of persons, without any perceptible interval of time.
2. Those bodies, which are conductors of electricity, are
Li also conductors of the galvanic fluid, as the metals, charcoal,
and a variety of liquids. Again, it is not transmitted by glass,
j sulphur, and the whole class of electrics, which do not con-
) i vey ordinary electricity. Among liquids, those only are con-
il ductors of electricity and galvanism, which contain oxygen as
one of their elements f .
•» Phil. Mag. xlv. 261.
f Cxuickshank, in Nicholson's 4to. Journal, iv. 258,
132
ELECTRO-CHEMISTRY.
CHAP. VlL
3. The galvanic fluid passes through air and certain otheT
non-conductors, in the form of sparks ; accompanied with a
snap or report ; and, like the electric fluid, it may be made
to inflame gun-powder, phosphorus, and mixtures of hydro¬
gen and oxygen gases. It has been found, also, by Mr. Chil¬
dren, that in the V oltaic apparatus there is, what is called in
electricity, a striking distance . With a power of 1250 pairs
of four inch plates, he found this distance to be one 50th of
an inch, the thickness of a plate of air, through which the
galvanic discharge is able to pass in the form of a spark.
Increasing the number of plates, the striking distance will be
greater; and the reverse when it is diminished. It is also
increased by rarefying the air, through which the spark is
transmitted.
4. The Voltaic apparatus is capable of communicating a
charge to a Leyden jar, or even to a battery. If the zinc end
of a pile (whether it be uppermost or the contrary) be made to
communicate with the inside of a jar, it is charged positively.
If circumstances be reversed, and the copper end be similarly
connected, the jar is charged negatively*. The shocks do
not differ from those of a jar or battery, charged to the same
intensity by a common electrical machine.
5. Galvanism, even when excited by a single galvanic circle
only (such as a piece of zinc, a similar one of copper, and a
piece of cloth moistened with a solution of muriate of am- i
monia), distinctly affects the gold leaf of the condensing elec¬
trometer. If the zinc end be uppermost, and be connected
directly with the instrument, the electricity indicated is posi¬
tive ; if the pin of the electrometer touch the copper, the
electricity is negative. A pile consisting of sixty combina- •
tions produces the effect still more remarkably f.
6. The chemical changes produced by galvanic and com¬
mon electricity, so far as they have hitherto been examined,
are precisely similar. These will form the subject of the fol¬
lowing section.
* Cuthbertson's Practical Electricity and Galvanism, p. 261 ; Volta, in
Nicholson's Journal, 8vo. i. 140 ; Van Marum, in Philosophical Magazine,
xii. 162.
+ Nicholson, 8vo. i. 139, andii. 281 ; Cuthbertson, p. 264.
SECT. III.
ELECTRO-CHEMISTRY.
193
SECTION III.
On the Chemical Agencies of Electricity and Galvanism .
The effects of the electric or galvanic fluids, in producing
chemical decomposition, cannot be described, without intro¬
ducing to the reader the names of several substances, with
which, in the present state of his knowledge, he may be sup¬
posed to be unacquainted. This difficulty is unavoidable ; for
it is impossible to explain the general laws of electro-chemical
action, without a variety of particular instances. In general,
however, it will be found that a minute acquaintance with the
bodies, which are brought in illustration, is by no means essen¬
tial ; and that it is sufficient to consider them as composed
simply of two ingredients, which are in opposite electrical
states, and are subject to the laws of electrical attraction and
repulsion.
The most simple chemical effect, produced alike by the
agency of electricity and galvanism, is the ignition and fusion
of metals . When a piece of watch-pendulum wire is placed
in the circuit of a common electrical battery, containing not
less than three or four square feet of coating, at the moment
of the discharge the wire becomes red-hot ; but continues so
only for a few seconds ; no longer, indeed, than if it had been
ignited in any other way *. The same effect may be produced
by making a piece of wire the medium of communication be¬
tween the opposite extremities of a galvanic trough ; but, in
this case, the heat continues sensibly longer, than when it
is excited by an electrical explosion. Indeed a platina wire
may be kept ignited in vacuo , for an unlimited time, by Vol¬
taic electricity. Water, surrounding a wire so placed, may
be made to boil briskly.
By means of his large battery, Mr. Children not only
! ignited wire of considerable thickness; but a bar of platina,
■i-th of an inch square and 2^ inches long, was ignited, and
1 even fused at one end. The facility of being ignited in the
* On the quantity of coated surface required for igniting different lengths
of wire, the reader may consult Mr. Cuthbertson’s book, p. 161, &c.
VOL. T.
O
194
ELECTRO-CHEMISTRY.
CHAP. VI Ir
different metals appeared to be inversely proportional to their
power of conducting heat. Thus platina, which has the lowest
conducting power, was most easily ignited ; and silver, which
conducts heat better than any other metal, was ignited with
greater difficulty than any of the rest.
It does not appear, however, that a very powerful combi¬
nation is required to produce ignition, if the wire be made of
proportionately small diameter. Dr. "Wollaston has ascer¬
tained that a wire ^Vo °f an inch in diameter may be ignited
by a single zinc plate only one inch square, provided each of
its surfaces be opposed to a surface of copper or some other
metal. The liquor which he employed was a mixture of one
measure of sulphuric acid with 50 measures of water. Any
farther diminution in the diameter of the wire he found to be :
unfavourable to the effect, in consequence of the increase of
the cooling power of the atmosphere
When the power of an electrical battery is increased, me¬
tallic wires, by transmitting the discharge through them, may
be melted and dispersed in the form of smoke, or of an im¬
palpable powder lighter than air. The galvanic discharge,
also, is capable of fusing metallic wires ; but being less violent,
it does not scatter their particles to a distance. Even wire
from the most infusible of the metals, platina, acquires a white
heat, and melts into globules.
With a still more powerful electrical battery (one for ex- 1
ample containing about 18 square feet) metallic wires are not
only melted, but undergo absolute combustion . Lead and tin
wire emit a yellow light, and copper and silver a green one. .?
If the experiment be made on wire confined in a glass receiver,
which contains a measured quantity of air, the bulk of the air,
and its proportion of oxygen, are both found to be dimi¬
nished f . The metals are converted into oxides of different
colours ; lead, tin, and zinc, into white oxides ; platina, gold,
silver, and copper, into oxides of a dark colour. The experi¬
ment may be pleasingly varied by passing the discharge
through wires, stretched over panes of glass or sheets of paper,
at a small distance from their surface. The metallic oxide
* Thomson's Annals, vi. 209.
+ Cuthbertson, p. 199.
SECT. III.
ELECTRO-CfiEMISTRlf.
1'95
which is produced is forcibly driven into the glass or paper ;
and produces beautiful figures* varying in colour with the
metal employed *.
The combustion of metals may be effected, also, by galvanic
electricity ; but for this purpose the form of very thin leaves
is preferable to that of wire. The plates, composing the ga!»
vanic trough, should, for this purpose, be not less than four
inches square, the larger, indeed, the better; and several
troughs should be joined together, so as to form an aggregate
of not less than 100 or 1 50 pairs of plates. The galvanic in«
fluence is to be conveyed by wires brought from each extremity
of the arrangement, and placed in contact with the opposite
surfaces of the leaf. For the protection of the fingers, the
wires should be inclosed in glass tubes. When thus exposed,
the metals burn, or rather deflagrate, with great brilliancy.
Gold emits a very vivid white light, inclining a little to blue,
and leaves an oxide, whose colour verges towards that of ma¬
hogany. Copper presents similar phenomena.
The flame of silver is a vivid green, somewhat like that of
a pale emerald, and the light is more intense than that of
gold. Lead gives a vivid light of a dilute bluish purple®
Tin a light similar to that of gold ; and zinc a bluish white
flame fringed with redf. In all these cases, provided the
power be sufficiently strong, the deflagration is kept up, for
some time, without intermission.
But a much more remarkable action is exerted by the elec¬
tric and galvanic fluids, in disuniting the elements of several
combinations. One of the first discoveries of the chemical
agency of the pile was its power of decomposing water. Two
pieces of any metallic wire are thrust through separate corks,
which are fitted into the open ends of a glass tube in such a
way, that the extremities of the wires, when the corks are in
their places, may not be in contact, but may be at the distance
from each other of about a quarter of an inch (see fig. 77, a)*
* Cuthbertson, p. 226 ; and Wilkinson’s Elements of Galvanism, in the
9th plate of which these appearances are represented,
t Philosophical Magazine, xi. 284, and xv, 96.
o 2
196
ELECTRO-CHEMISTRY.
CHAP. VII.
If the parts of the wire, which project from without the tube,
be made to communicate, the one with the zinc or positive
end, and the other with the copper or negative end, of a gal¬
vanic battery, a remarkable appearance takes place. The wire,
connected with the zinc or positive end of the pile or trough,
where it is in contact w ith* the water, if of an oxidable metal,
is rapidly oxidized ; while from the negative wire a stream of
small bubbles of gas arises. But if the wires employed be of
a metal which is not susceptible of oxidation, such as gold
or platina, gas is then extricated from both wires, and, by a
simple contrivance, may be separately collected. The appa¬
ratus for this purpose is shown by fig. 76, where the wires p
and ?z, instead of being introduced into a straight tube, are
inclosed in a syphon, and terminate before they reach the end,
in which a small hole is to be ground. When a stream of
galvanic electricity is made to act upon water thus confined,
oxygen gas is found, at the close of the experiment, in the leg
connected with the positive end of the battery, and hydrogen
gas in that connected with the negative end ; and in the pro¬
portions which, by their union, compose water. At an early
period of the inquiry, it was found, however, by Mr. Cruick-
shank, that the water surrounding the positive wire became
impregnated with a little acid ; and that around the negative
wire with a little alkali. If instead of water we employ a me¬
tallic solution, the metal is revived round the negative wire n,
and no hydrogen gas is liberated.
The gases constituting water, it was afterwards discovered
by Sir H. Davy, may be separately produced from two quan¬
tities of water, not immediately in contact with each other.
The fact is of peculiar importance, from its resemblance to
other more recent ones, which have led that distinguished
philosopher to the discovery of the general laws of electro¬
chemical action. Two glass tubes (p and ?z, pi. ix. fig. 79),
about one third of an inch diameter and four inches long,
having each a piece of gold wire sealed hermetically into one
end and the other end open, were filled with distilled water,
and placed inverted in separate glasses fijled, also, with that
fluid. The two glasses, a and b , were made to communicate,
either by dipping the fingers of the right hand into one glass.
SECT. III.
ELECTRO-CHEMISTRY.
197
and those of the left into the other, or by interposing fresh
animal muscle, or a living vegetable, or even moistened thread,
as shown at c. The gold wires, projecting from the sealed
ends of these tubes, were then connected, the one with the
positive, the other with the negative end of the trough. Gas
was immediately evolved from both wires. At the close of the
experiment, in the tube/j oxygen gas was found ; in the negative
tube n hydrogen. The proportions by measure were, as nearly
as possible, those which result from the decomposition of
water, viz . two of hydrogen to one of oxygen gas *. Now if
these gases arose, as they necessarily must, from the decom¬
position of the same portion of water, that portion of water
must have been contained either in the tube p or in the tube n.
In the former case, the hydrogen gas, found after the process
in ?z, must have passed invisibly from p to n, through the in¬
termediate substance c. Or, if the water was decomposed in
w, then the reverse process must have happened with respect
to the oxygen ; and it must have been transmitted, in a like
imperceptible manner, from n to Facts of this kind, evinc¬
ing the transference of the elements of a combination, to a
considerable distance, through intervening substances, and hi
a form that escapes the cognizance . of our senses, however
astonishing, it will appear from the sequel, are sufficiently nu¬
merous and well established. It appears, also, from the ex¬
periments of Mr. Porrett, that water may be forced, contrary
to its gravity, through the compact substance of a bladder,
from the positive to the negative wire of a galvanic battery,
composed of plates only 1^ inch square f.
Different chemical compounds require, for the disunion of
their elements, galvanic arrangements of various powers and
intensities. The decomposition of water is easily effected by
a series of fifty pairs of plates, each one or two inches square.
But for those which remain to be described, instruments of
much greater power are necessary.
The apparatus, employed in the masterly experiments of
Sir H. Davy, which have laid the groundwork of this new
field of science, was extremely simple. In cases, where liquid
* Nicholson’s Journal, 4to, iv. 276,
+ Thomson’s Annals, viii. 74,
ELECTRO-CHEMISTRY.
CHAP* VII,
substances were operated upon, he employed occasionally the
agate cups p and ft, fig. 80, each of which was capable o^
holding about sixty grains of water. They were connected
together, as shown in the figure at a , by the fibres of a pecu-
liar flexible mineral called amianthus ; and into each was in¬
serted a platina wire, the bent extremity of which is seen, in
each figure, projecting above the cup. When the vessels
were in actual use^ the wire of p was connected with the zinc
or positive end of a powerful galvanic series ; and that of n
with the copper or negative extremity. For the agate cups
two hollow gold cones wrere occasionally substituted (p and ft,
fig. 81), the wire projecting from p being connected with the
positive, and that from n with the negative end of a trough
or series of troughs. Solid bodies were submitted to the
galvanic influence, either by immersing small pieces of them
in the gold cones : or, at other times, by making the cups
themselves of the substance intended to be decomposed. Or
if it was desirable to preserve them from contact with water,
they were laid on a small insulated dish of platina, with the
inferior surface of which, immediately under the substance
used, a wire from one end of the battery was connected,
while the substance itself was made to communicate bv another
%J
wire, with the opposite extremity of the apparatus.
When the gold cones were both filled with a solution of
sulphate of potash (a salt composed of potash and sulphuric
acid), after exposure, during a sufficient time, to a powerful
galvanic arrangement, pure potash was found in the negative
cone ft, and sulphuric acid in the positive cone p. The de¬
composition was even quite complete ; for the liquid in n con¬
tained no acid, and that in p no alkali.
The experiment was repeated with several other neutral
salts * ; and with the invariable result, that the acid collected
in the positive cone, and the alkali in the negative one.
Strong solutions, or those in which the salt bore a considerable
proportion to the water, were more rapidly acted upon than
* Minute directions for exhibiting the transfer of acid and alkali, by
means of a power not exceeding thirty pairs of two inch plates, are gi vein
fey Mr. Singer. (Nicholson’ s Journal, xxiv. 178.)
1
'A
SECT, III.
ELECTRO-CHEMISTRY.
199
r
i
»
&
i
weak ones. Metallic salts were, also, decomposed. The
acid appeared, as before, in the positive cone, and the metal
was deposited, sometimes with a little oxide, in the negative
one.
Salts, which are either insoluble, or very sparingly soluble,
in water, had their elements disunited in the following manner.
Cups were constructed of them, precisely resembling the
gold cones, which, as the salts were hard and compact in
their texture, was easily effected. These, after being filled
with water, were connected, by platina wires, with the oppo¬
site ends of a galvanic battery, the vessels themselves com¬
municating, as before, by means of moistened amianthus.
At the conclusion of the experiment, sulphuric acid (when
the cups were made of sulphate of lime) was found in the
positive cup, and lime water in the negative one. Sulphate
of strontites, fluate of lime, and sulphate of barytes, were
decomposed, though less easily, by the same expedient. In
all these cases the acid element was found at the positive side,
and the earthy one at the negative side, of the arrangement.
These facts evidently point out a transference of the ele¬
ments of combinations from one electrified vessel or surface
to another differently electrified. But the principle is made
much more apparent by a little variation of the experiment.
Thus, if solution of sulphate of potash be electrified in the
positive cone p9 water alone being contained in ?z, after a suf¬
ficient continuance of the electrical action p, will be found to
contain diluted sulphuric acid; and the potash will be dis¬
covered in the water of n. The alkali must necessarilv, there-
fore, have passed, in an imperceptible form, along the con¬
necting amianthus from the vessel p to the vessel n. Reversing
the experiment, and filling n with solution of sulphate of pot¬
ash, the alkali remains in this cone, and the acid is transferred
to the opposite side p. ' In one experiment, in which nitrate
of silver was placed in the positive cup, and pure water in
the negative one, the whole of the connecting amianthus was
covered with revived silver.
In the farther prosecution of the inquiry, Sir H. Davy
succeeded in discovering a still more extraoi dinary series of
facts. When an intermediate vessel (i, fig. 82) was placed
4
200
ELECTRO-CHEMISTRY.
CHAP# VII.
between the positive and negative cups p and n> and was con¬
nected with both of them by moistened amianthus, it was
found that acids may actually be made to pass from n to
through the intermediate solution in i, without combining
with it. Thus, solution of sulphate of potash being put into
the negative cup n9 solution of pure ammonia into i, and pure
water into p, in half an hour sulphuric acid was found in the
water of the positive cup, to have reached which it must have
been transferred from n through the intermediate solution of
ammonia. Muriatic acid, also, from muriate of soda, and
nitric acid from nitrate of potash, were transferred from the
negative to the positive side through an interposed solution of
alkali. And contrariwise, alkalies and metallic oxides w^ere
transmitted from the positive to the negative side, through
intervening solutions of acids.
It is necessary, howrever, that the solution, contained in
the intermediate vessel i, should not be capable of forming an
insoluble compound with the substance intended to be trans¬
mitted through it. Thus sulphuric acid, in its passage from
sulphate of potash in the negative cup, through the vessel i
containing a solution of pure barytes, is detained by the
barytes, and falls down in the state of an insoluble compound
with that earth.
Bodies, the composition of which is considerably more
complicated, are, also, decomposed by galvanic electricity.
Thus from certain minerals, containing acid and alkaline
matter in only very minute proportion, these ingredients are
separately developed. Basalt, for example (a kind of stone
which, in 100 grains, contains only 3-L grains of soda and
half a grain of muriatic acid), gave, at the end of ten hours,
evident traces of alkali round the negative, and of acid round
the positive wire. A slip of glass, also, negatively electrified
in one of the gold cones, had soda detached from it, and
sustained a loss of weight.
It may now be understood, why, by the agency of gal¬
vanism on water, alkali appears at the negative and acid at
the positive wire. The fact was, for some time, not a little
perplexing to Sir H. Davy ; till, at length, he ascertained
that all water, however carefully distilled, contains neutral
SECT. HI.
ELECTRO-CHEMISTRY.
201
salts in a state of solution. From these impurities, the alka¬
line and acid elements are separated, agreeably to a law,
which has already been explained. In the same way, also,
the muriatic acid and alkali are accounted for, which some
chemists have obtained by galvanizing what was before con¬
sidered as pure water ; a fact which has been urged in proof
of the synthetical production of both those bodies. Abso¬
lutely pure water, it has been demonstrated by Sir H. Davy,
yields nothing but hydrogen and oxygen gases.
All the effects of galvanic arrangements, in producing
i chemical decompositions, it has been found, may be obtained
j by ordinary electricity. Its adaptation to this purpose was
1 first successfully attempted by Dr. Wollaston *. The appa-
j ratus, which he employed, was similar to that already repre-
5 sented (fig. 77, a)9 excepting that the wires, instead of being
2 exposed to the fluid, contained in the tube, throughout their
i whole length, were covered with wax, and the points only
n were laid bare. Or (what was found to answer still better)
ff the wires were inclosed in capillary tubes, which were sealed
i at their extremities, and then ground away, till the points
[j alone were exposed. The conducting wires, thus arranged,
i were then introduced into a tube, or other vessel containing
[i the liquid to be operated on, and were connected, the one
-f with the positive, the other with the negative, conductor of
i an electrical machine, disposed for positive and negative elec-
4 tricity f . When solution of sulphate of copper was thus
• electrized, the metal was revived round the negative pole.
On reversing the apparatus, the copper was re-dissolved, and
j appeared again at the other wire, now rendered negative.
When gold wires, from yi- to TTVo of an inch in dia»
i meter, thus inclosed, were made to transmit electricity, a
succession of sparks afforded a current of gas from water,
i When a solution of gold in nitro-muriatic acid was passed
I through a capillary tube ; the tube then heated to drive oft’
[| the acid; and afterwards melted and drawn out, it was found
* Philosophical Transactions, 1801.
f See Cuthbertson’s Practical Electricity.
202
ELECTRO-CHEMISTRY.
CHAP. VII.
that the mere current of electricity, without sparks, evolved
gas from water.
Sir H. Davy has since proved that by a similar apparatus,
solution of sulphate , of potash is decomposed, potash appear¬
ing at the negative, and sulphuric acid at the positive pole*.
SECTION IV.
Theory of the Changes produced by Galvanic Electricity ,
A fact of considerable importance in explaining the phe«
nomena that form the subject of the last section was discovered
several years ago by Mr. Bennett, and has since been con¬
firmed by the experiments of Volta and Davy. Different
bodies, it is found, acquire, when brought into contact either
by their whole surfaces or by a single point, different states
with respect to their quantities of electricity. The best method
of performing the experiment is to take two discs or plates,
the one of copper, the other of zinc, each about four inches
diameter, and furnished with an insulating glass handle ; to
apply them for an instant to each other by their flat faces ;
and afterwards, to bring them separately into contact wfltli
the insulated plate of the condensing electrometer. The in¬
strument indicates, by the divergence of its gold leaves, the
electricity acquired by each of the plates, which in the zinc
plate is shown to be positive, and in the copper plate negative f.
It had been established, also, by Sir H. Davy, in 1801,
that when a galvanic arrangement of the second kind is con¬
structed, by alternating metallic plates with strata of different
fluids, alkaline solutions always receive electricity from the
metal, and acids on the contrary transmit it to the metal.
When an arrangement, for example, is made of water, tin,
and solution of potash, the current of electricity is from the
tin to the alkali. But, in an arrangement of nitric acid, tin,
* Philosophical Transactions, 1806.
f Volta, in Nicholson’s Journal, 8vo. i. 136. Wilkinson, ii. 40, 50, 13V
Cuthbertson, 267,
SECT, IV,
ELECTRO-CHEMISTRY.
203
i and water* the circulation of electricity is from the acid to
fi the tin. If then the alkali, after having acquired electricity
from the metal, could be suddenly separated from the combi-
D nation, there can be no doubt that it would be found in a
0 positive state. For the contrary reason, the acid, having
'{ given electricity to the metal, must, if it could be detached,
o be found negative.
Still more satisfactory evidence has been since obtained of
li the electrical state of the acids and alkalies, by examining
n what kind of electricity they impart to an insulated metallic
q plate. Various dry acids, being touched on an extensive
i surface by a plate of copper insulated by a glass handle, the
q copper was found after contact to have become positively elec-
j trifled, and the acid negatively. On the contrary, making the
9 experiments with dry earths in a similar manner, the metal
d became negative. The alkalies gave less distinct results, owing
j to their attraction for moisture. Bodies, moreover, possessing
3 opposite electrical energies towards one and the same body,
B are found to possess them with regard to each other. Thus
i when lime and oxalic acid were brought into contact, the
9 earth was found to be positive, and the acid negative. Sulphur
B appears to be in the positive state. Oxygen, judging from
J those compounds in which it is loosely combined, is negative;
a and hydrogen, by the same test, positive.
Now, if the common laws of electrical attraction and re-
q pulsion operate, as there is every reason to believe they must,
3 among bodies so constituted, it will follow that hydrogen, the
a alkalies, metals, and oxides, being positively electrified, will
1 be repelled by surfaces which are in the same state of electri-
j city as themselves, and wall be attracted by surfaces that are
i negatively electrified. And, contrariwise, oxygen, and the
3 acids (in consequence of the oxygen they contain), being in a
i negative state, will be attracted by positive surfaces and re-
j pelled by negative ones.
To apply this theory to the simplest possible case, the de¬
composition of water, the hydrogen of this compound, being
: itself positively electrified, is repelled by the positive wire
i and attracted by the negative one; while, on the contrary,
) oxygen, being negative, is repelled by the negative wire, and
ELECTRO-CHEMISTRY,
^04?
«\V
CHAP* VII*
attracted by the positive one. The flame of a candle, which
consists chiefly of ignited charcoal, when placed between a
positive and negative surface, bends towards the latter; but
the flame of phosphorus, consisting chiefly of acid matter, j
when similarly placed, takes a direction towards the positive
surface. In the case of neutral salts, the negative acid is
attracted by the positive wire ; and the positively electrified
alkali by the negative wire.
Thus then a power has been discovered, superior in its
energy to chemical affinity, and capable either of counteract¬
ing it, or of modifying it according to circumstances. The
chemical attraction between two bodies may be destroyed, by
giving one of them an electrical state opposite to its natural
one ; or the tendency to union may be increased, by exalting
the natural electrical energies.
All bodies, indeed, that combine chemically, so far as they
have hitherto been examined,, have been found to possess
opposite states of electricity. Thus copper and zinc are in
opposite states to each other ; so are gold and mercury ; sul¬
phur and metals, acids and alkalies. By bringing two bodies
into the same electrical state, which were before capable of
union, we destroy their tendency to combination. Thus
zinc or iron, when negatively electrified, will not unite with
oxygen. Even after combination, it is thought by Sir H.
Davy not improbable, that bodies may still retain their pecu¬
liar states of electricity. If oxygen prevail, in any com¬
pound, over the combustible or positive base, the compound
is negative, as in certain metallic oxides. But the combustible
ingredient may be in such proportion, as to predominate,
and to give to the compound a positive energy, When pre¬
cise neutralization is attained, bodies that had before exhibited
electrical effects are deprived of this property.
It is an interesting question, but one which can scarcely be
determined in the present state of the science, whether the power
of electrical attraction and repulsion be identical, as Sir H.
Davy has suggested, with chemical affinity; or whether it
may not rather be considered, like caloric, as a distinct force,
which only modifies that of chemical attraction. On the for¬
mer hypothesis, two bodies, which are naturally in opposite *
6
SECT. V.
ELECTRO-CHEMISTRY.
205
: electrical states, may have these states sufficiently exalted, to
i give them an attractive force superior to the cohesive affinity
opposed to their union : and a combination will take place,
{ which will be more or less energetic, as the opposed forces are
ji more or less equally balanced. Again, when two bodies, re-
•i pellent of each other, act upon a third with different degrees
[( of the same electrical energy, the combination will be deter-
i mined by the degree. Or, if bodies, having different degrees
h of the same electrical energy with respect to a third, have like-
'i wise different energies with respect to each other, there may
i be such a balance of attracting and repelling forces as to pro-
fl duce a triple compound.
This hypothesis, it is remarked by Sir H. Davy, agrees ex-
•J tremely well with the influence of mass, which has been so
>i well illustrated by Berthollet ; for many particles, acting
i feebly, may be equal in effect to fewer acting more powerfully,
m Nor is it at all contradictory to the observed influence of caloric
ij over chemical union ; for an increase of temperature, while it
I gives greater freedom of motion to the particles of bodies,
gj exalts all their electrical energies. This Sir H. Davy ascer-
& tained with respect to an insulated plate of copper and another
1 of sulphur, when heated below 212° Fahrenheit ; and at a still
1 higher temperature these bodies, as is well known, combine
ii with the extrication of heat and light, the usual accompani-
q ments of intense chemical action.
On the supposition that electricity is a force, which only mo-
i. difies the action of chemical affinity, we may regard it, when
; it promotes combination, as producing this effect by counter-
d acting cohesive attraction. Whon it impedes combinations,
: or destroys those which are already formed, it probably acts
} as a force co-operating with elasticity.
SECTION V.
Theory of the Action of the Galvanic Pile .
Two theories have been framed to account for the pheno-
iinena of the Galvanic Pile, and of all similar arrangements.
20 G ELECTRO-CHEMISTRY. CHAP. VI?. ,
The first, originating with Volta, was suggested by the fact* ,
which may be considered, indeed, as fundamental to it — that
electricity is excited by the mere contact of different metals..
W hen a plate of copper and another of zinc are made to »
touch by their flat surfaces, as was stated in the last section,
the zinc, after separation, exhibits positive electricity, and the
copper negative. It is natural, therefore, to conclude that a
certain quantity of electricity has moved from the copper to
the zinc. On trying other metals, Volta found that similar
phenomena take place ; and by a series of experiments he
was led to arrange their powers in the following order, it
being understood that the first gives up its electricity to the
second ; the second to the third ; the third to the fourth, and
so on.
Silver.
Copper.
Iron.
Tin.
Lead.
Zinc.
The metals, then, have been denominated by Volta, from
this property, motors of electricity; and the process, which
takes place, electro-motion , a term since sanctioned by the
adoption of it by Sir H. Davy.
It is on this tranference of electricity from one body to ano¬
ther by simple contact, that Volta explains the action of the
instrument discovered by himself, and of all similar arrange¬
ments. The interposed fluids, on his hypothesis, have no
effect as chemical agents in producing the phenomena, and
act entirely as conductors of electricity. Without disputing,
however, the accuracy or value of the facts which suggested
his theory, it is sufficient for its refutation that it is irrecon-
cileable with other phenomena ; and especially with the obser¬
vation, that the chemical agency of the liquids, on the more
oxidizable metal of galvanic arrangements, is essential to their
sustained activity. It has been proved, indeed, that the phe¬
nomena begin and terminate with the oxidation ; and that the
energy of the pile bears a pretty accurate proportion to the
SECT. V. ELECTRO-CHEMISTRY, 20?
rapidity of the process. Hence it seems, on first view, an
obvious inference, that the oxidation of the metal is the pri¬
mary cause of the evolution of electricity in galvanic arrange-
ments. It has been proved, however, that it is not ne-
i cessary to the excitement of electricity, that the amalgam
t should be oxidated ; for the machine continues to act when
t inclosed in hydrogen gas or carbonic acid ; and the electric
* column of M. de Luc is composed of dry substances. Even
in this instrument, the oxidation of the metals appears to be
> essential to its activity, for when the column is hermetically
> confined in a given portion of air, the phenomena cease in
I time, in consequence of the loss of its oxygen.
But though the chemical agency of the fluids which are
> employed is now admitted, on all hands, to be essential to the
> excitement of this kind of electricity, yet is by no means uni-
r versally agreed that we are to consider it as the first in the
}) order of phenomena. It has been suggested by Sir H. Davy,
5 as a correction of the theory of V olta, that the electro-motion,
> occasioned by the contact of metals, is the primary cause of
I the chemical changes ; and that these changes are in no other
t way efficient, than as they restore the electric equilibrium.
l| To explain this, let us suppose that in any three pairs of plates
j of a galvanic trough, the zinc plates x 1, x 2, z 3 (fig. 78), are
i in the state of positive, and the copper plates c 1, c 2, c 3, in
1 that of negative electricity. The liquid, in any cell after the
\ first, will be in contact, on the one side, with positively elec-
i trifled zinc, and on the other with negatively electrified cop-
;[ per. And if the elements composing the fluid be themselves
t* in different states of electricity, the negatively electrified ele-
r: ment will be attracted by the zinc, and the positively electrified
o element by the copper. Thus when solution of muriate of
a soda in water is the fluid, the oxygen and the acid will pass
: to the zinc or positive plate, and the alkali to the copper
i one ; while the hydrogen, having no affinity for copper,
o escapes. The electric equilibrium will be restored, but only
i for a moment ; for, as the interposed fluid is but a very imper¬
il feet conductor of electricity, the zinc and copper plates w ill,
! by their electromotive power, again assume their states of op-
1 posite electricity ; and these changes will go on, as long as
208
ELECTRO-CHEMISTRY.
CHAP. VII,
any muriate of soda remains undecomposed. In a Voltaic ar¬
rangement, therefore, the electrical energies of the metals
with respect to each other, or to the substances dissolved in
water, are the causes disturbing the equilibrium; and the
chemical changes are the causes that restore it.
No theory of the galvanic pile, however, can be considered
as complete, that does not account for the accumulation of
electricity at the zinc end of the apparatus. On the theory
that the oxidation of the zinc is the source of the evolved elec¬
tricity, the fact has been ingeniously explained by Dr. Bos-
tock. He takes it for granted that the electric fluid has an
affinity for hydrogen ; and supposes that the electricity, evolved
at the surface of the first zinc plate, is carried, united to
hydrogen, through the fluid of the cell to the opposite
copper plate. Here the hydrogen and electricity separate;
the former flies off in the state of gas, and the latter passes |
outwards to the next zinc plate. Being in some degree accu¬
mulated in this plate, it is disengaged by the action of the j
fluid in a more concentrated state than before. And in the
same manner, by multiplying the number of pairs, it may be
made to exist, in the zinc end of the pile, in any assignable
degree of intensity.
On this theory, the electricity evolved is actually generated
by the chemical action of the interposed fluids on every zinc
plate of the series ; and its accumulation is the aggregate of I
what is thus evolved. The concentration, which takes place
at the zinc end of the arrangement admits, however, of being
explained by the hypothesis of Volta, especially as modified
by Sir H. Davy. Taking the first cell as an example, the
fluid interposed between the positive zinc plate z 1, fig. 78,
and negative copper plate c 2, being itself a conductor of
electricity, must in time produce an equilibrium between these
two plates ; but this can only be done by the passage of a cer¬
tain quantity of electricity across the fluid. The absolute
quantity of electricity will, therefore, be diminished in the
first pair, and increased in the second. In like manner, the
second zinc plate will give up part of its electricity to the
third copper plate, and the second pair of plates will be de¬
prived of part of its electricity. The electricity, thus lost by
SECT. V.
ELECTRO-CHEMISTRY.
2 09
the second pair, it will regain from the first pair of plates.
By multiplying, in this way, the number of plates, every suc¬
cessive pair, as we advance in the series, has a tendency to
diminish the quantity of electricity in the first; and to have
its own state of electricity proportionally exalted.
When a communication is made between two extremities of
a series, for example between z3 or its contiguous cell, and
c* 1 *, the opposite electricities tend to an equilibrium. The
third pair gives up a share of its electricity to the first; and
the intermediate pair, being placed between equal forces, re-
[ mains in equilibrio. Hence, in every galvanic arrangement,
i there is a pair of plates at the centre, which is in its natu-
i ral state of electricity. The effect of such a communica-
t tion must necessarily be to reduce the pile to a state of inac-
jj tivity, if there did not still exist some cause sufficient to tie-
3 stroy the equilibrium. On the hypothesis of Volta, this can
J be nothing else than the property of electro-motion in the
a metals, which originally produced its disturbance.
Such are the hypotheses that have been framed to explain
[| the phenomena of the Voltaic pile. In the present state of
If the science, neither of them is entitled to be received as alto-
i| gether satisfactory; and I have stated them rather with the
[\ view of exciting than of satisfying inquiry #. On the theory
k of galvanic electricity, it only remains to point out its differ-
f| ence from the electricity developed by ordinary processes ; and
oj to explain the different effects, which are produced by varying
cl the size of the plates in galvanic arrangements.
Though the identity of common and galvanic electricity
a appears to be sufficiently established, yet in some of their phc-
)i nomena, which have already been described, there is a con-
)i siderable difference. To explain these, it was long ago sug-
* The reader, who wishes to pursue the subject, may consult an essay
- bv the author, in Nicholson’s Journal, xxxv 259: M. De Luc’s papers,
J xxxii. 2^1, and xxxvi. 97 ; Mr. Singer on the Electrical Column, xxxvi. 373,
land his work on Galvanic Electricity ; Dr. Rostock’s Essay in Thomson’s
Annals, iii. 32; Sir H. Daw’s chapter on Electrical Attraction and Repul-
• sion, in his Elements ot Chem. Philos, p. 125; and the 1st. vol, of Gay
i Lussac and Thenard’s Recherches.
VOL. 1. P
210 ELECTRO-CHEMISTRY. CHAP. YIIv
gested by Mr. Nicholson #, that the electricity, excited by the
common machine, is developed in much smaller quantity, but
in a higher state of concentration or intensity than the elec¬
tricity of galvanism. Hence, its velocity is much more rapid;
and hence it readily passes through plates of air and other
non-conductors, that are scarcely permeable by galvanic elec¬
tricity. By virtue of the same property it disperses the metals,
in the form of smoke; while the utmost effect of a Voltaic
arrangement is to melt them into globules. By doubling the
quantity of galvanic electricity, also, we ignite only a double
length of metallic wire, and the ignition is more permanent y.
but the intensity of common electricity is such, that by
doubling its quantity we ignite four times the length of wrire,
and the effect is little more than momentary f.
The comparative quantities of electricity evolved by the
common machine and by a Voltaic apparatus, have been made
a subject of calculation by Mr. Nicholson. A pile consisting
of 100 half crowns, with the same number of pieces of zinc*
produces, he found, 200 times more electricity than can be
obtained, in an equal time, from a 24 inch plate machine in
constant action. Van Marum has, also, observed that a single
contact of a Leyden jar or battery with a Voltaic pile charges
it to the same degree, as six contacts with the prime conductor
of a powerful machine.
It might naturally be expected that a proportion would be
observed between the quantity of surface composing galvanic
arrangements, and their power of action; and such, with
some limitation, is the fact. With plates of the same size,
the effect, generally speaking, is proportional to the number.
But by enlarging the size, without increasing the number,
neither the shock nor the power of decomposing water and
other imperfect conductors, is proportionally increased. A
remarkable proof of this is, that Mr. Children’s great battery
of 20 double plates, 4 feet by 2, had no more effect on the
human body, or in decomposing water, than a battery con¬
taining the same number of small plates. On the contrary,
* See his Journal, 4to. iv. 244.
I Cuthbertsorn, p, 27 8,
\ SECT. V.
ELECTRO-CHEMISTRY.
211
i to obtain a great increase of effect in the combustion of metals,
i it is necessary to enlarge considerably the size of the plates.
Thus 100 plates of four inches square produce, in this way,
] an incomparably greater effect, than the same surface divided
i into four times the number.
The effect of multiplying the number of plates, it has
s already been observed, is, that we obtain electricity of a higher
i intensity, and it was supposed by Volta * that the proportion
i is, as nearly as can be judged, an arithmetical one. If, for
i example, we have a certain intensity with 20 pairs, it should
I be doubled by 40, trebled by 60, and so on. It has been
i shown, however, by Sir H. Davy f, that by increasing the
i number of plates, the quantities of gas, evolved from water,
j were nearly as the squares of the numbers. By a sufficient
j increase, the most astonishing effects may be produced. Thus
I the combination belonging to the Royal Institution, which
) contains 2000 double plates, each having a surface of 32 square
i inches, when in action, melts platinum, as easily as wax is
i melted by a candle, and fuses quartz, the sapphire, lime, and
i magnesia. By enlarging the size, without increasing the num-
j ber, it has also been shown that we gain, not in intensity,
n which remains exactly the same, but in quantity. Now, for
[i the combustion of metals what we principally want is a large
p quantity of electricity ; for as they are perfect conductors, it
I finds a ready passage through them even when of low inten¬
ds sity. On the contrary, to find its way through fluids and other
i imperfect conductors, it must be evolved in a high state of
3 concentration. The facts, therefore, accord sufficiently well
i with the explanation, to entitle it to be received as a probable
! hypothesis.
* Nicholson’s Journal, 8vo. i. 139.
t Elements of Chem. Philos, p. 15S,
2
2 12
CHAPTER VIII.
ALKALIES.
JLHE alkalies, in their pure state, are the products of che¬
mical operations, which will be described in the sequel. They
are distinguished by the following
General Oualities.
The properties, common to all the alkalies, may be shown
by those of a solution of pure potash.
(a) The alkalies change vegetable blue colours, as that of
an infusion of violets to green.
( b ) They have an acrid and peculiar taste.
(c) They serve as the intermedia between oils and water.
( d ) They corrode woollen cloth ; and, if the solution be
sufficiently strong, reduce it to the form of a jelly.
(e) They are readily soluble in water.
(f) The fixed alkalies unite with water, and form solid hy¬
drates.
SECTION I.
Pure Potash and pure Soda.
Art. 1. — Their Preparation and General Qualities.
To prepare pure potash, dissolve any quantity of American
or Dantzic pearlash in twice its weight of boiling water, and
add the solution, while hot, to an equal weight of fresh
quicklime, slaked with six times its weight of hot water. Boil
the mixture in an iron kettle, and continue stirring during
half an hour. Then separate the liquid alkali, either by fil¬
tering through calico or by subsidence ; and boil it to dryness
in a silver dish. Pour, on the dry mass, as much pure alco¬
hol as is required to dissolve it ; put the solution into a bottle*
SECT. I.
HYDRATED ALKALIES.
213
and let the insoluble part settle to the bottom. Then decant
the alcoholic solution of potash ; and distil off the alcohol in
an alembic * of pure silver, furnished with a glass head.
Pour the alkali, when in fusion, upon a silver dish, and, when
cold, break it into pieces, and preserve it in a well-stopped
bottle. If the distillation of the alcohol be not carried so far
the alkali will shoot, on cooling, into regular crystals, con¬
taining 53 per cent, of water.
From the electro-chemical researches of Sir H. Davy, it
appears that potash is not completely deprived of carbonic
acid, by any process hitherto employed for its preparation f .
Probably the method suggested by Darcet, of removing the
last portions of carbonic acid from an alkaline liquor by so¬
lution of barytes, after the full action of lime, would be found
effectual.
In the same mode may pure soda be prepared, substituting
the carbonate of soda for the pearlash.
These alkalies have the following properties :
(a) They powerfully attract moisture from the atmosphere,
or deliquiate.
(5) They readily dissolve in water, and produce heat during
d their solution, if the fused alkalies be employed ; but the crys¬
tallized alkalies generate cold, when dissolved.
(c) They are not volatilized by a moderate heat, and hence
have been called fixed alkalies.
(d) When melted with silex, in proper proportions and by
| a sufficient heat, they form glass.
Hydrated Alkalies.
It is necessary to observe that the alkalies, even after being
9 kept some time in fusion, contain a quantity of water in the
6i state of combination ; in other words, are hydrates . This
i discovery appears to be due to Darcet, who has established
i his claim very satisfactorily J. Various proportions of water
* The figure of an alembic may be seen in pi. i. fig. 2„
f -Philosophical Transactions, 1808, p. 355.
X 71 Ann. de Chim. p. 202.
214
ALKALIES.
CHAP. VIII.
and alkali have been assigned to these compounds. Ber-
thollet, in the 2d vol. of the Memoires d’Arcueil , states that
100 parts of solid potash, contain 13~ parts of water; but
Sir H. Davy* has raised it as high as from 17 to 19 per
cent. ; and Gay Lussac and Thenard allow about one fifth of
water in solid potash. One possible source of fallacy is, that
if the alkali contain soda, the proportion of water will ap¬
pear too great; because that alkali combines with more
water than potash. If, as Mr. Dalton suspects, the hydrate
of potash be a compound of 1 atom of potash + 1 atom of
water, its atom should weigh 56.5 ; and it ought to be com¬
posed of
84.9 potash f 84
15.1 water J or \l6
100 100
And it is remarkable, that according to the theoretical view
of Berzelius, potash, to become a hydrate, requires a quan¬
tity of water containing precisely as much oxygen as exists
in the alkali united with potassium ; that is, 100 parts of the
hydrate should contain 16.15 of water f.
There is also considerable difference in the statements re¬
specting Hydrate of Soda. Berard makes it contain 18.86
per cent, of water ; Darcet 28 ; and Sir H. Davy from 23 to
25 J. If the atom of soda weigh, as Mr. Dalton supposes,
28, and if the hydrate consist of 1 atom of soda + 1 atom
of water, the atom of hydrate of soda should weigh 36.5,
and the hydrate should be composed of
76.7 soda
23.3 water
100.
In these instances, the theoretical view, and the best practical
result, confirm each other.
* Elements, p. 326.
I Phil. Trans. 1811*
f 82 Ann. de Chim. p. 11.
SECT. 1.
HYDRATED ALKALIES.
215
It is often of importance to know the quantity of real alkali,
contained in solutions of different specific gravities. The fol¬
lowing Tables have been constructed by Mr. Dalton from
his own experiments, conducted with great attention to ac¬
curacy.
I. Table of the Quantity of Real Potash in watery Solutions of
different Specific Gravities .
Atoms of
Potash
W ater.
Potash
per cent,
by weight.
Potash
per cent,
by measure.
Specific
Gravity.
Congealing
point.
Boiling
point.
1
+
0
100
240
2.4
unknown.
unknown.
1
+
1
84
185
2.2
1000°
red heat.
1
+
2
72.4
145
2.0
500°
600°
1
+
O
O
63.6
1 49
1.88
340°
420°
I
+
4
56.8
101
1.78
220°
360°
1
+
5
51.2
86
1.68
150°
320°
1
4-
6
46.7
75
1.60
100°
290°
1
4“
7
42.9
65
1.52
70°
276°
1
4-
8
1 39.6
58
1.47
50°
265°
1
4-
9
36.8
53
1.44
40°
255°
1
+ 10
34.4
49
1.42
246°
32.4
45
1.39
240°
29.4
40
1.36
234°
26.3
35
1.33
229°
23.4
30
1 .28
224°
19.5
25
1.23
220°
16.2
20
1.19
218°
13
15
1.15
215°
9.5
10
1.11
214°
4.7
5
1.06
- « - - - -
213°
21 6
ALKALIES.
CHAP. VIII.
2. Table of the Quantity of Real Soda in watery Solutions of
diferent Specific Gravities.
Atoms of
Soda
Water.
Soda
per cent,
bv weight.
Soda
per cent,
by measure.
Specific
Gravity.
Congealing
point.
Boiling
point.
1 + o
100
230?
2.30?
1000°
unknown.
1 + 1
77.8
156
2.
500°
red hot.
1 4- 2
63.6
118
1.85
250°
600°
1 + 3
53.8
93
1.72
150°
400°
1 + 4
46.6
76
1.63
80°
300°
1+5
41.2
64
1.56
280°
1+6
36.8
55
1.50
265°
34
50
1.47
255°
31
45
1.44
248°
29
40
1.40
242°
26
35
1.36
235°
23
30
1.32
228°
19
25
+29
224°
16
20
1.23
220°
13
15
1.18
217°
9
10
1.12
214°
4.7
5
1.06
213°
Art. 2.— -Analysis of the two fixed Alkalies.
Though it had long been conjectured * that the fixed alkalies
are not simple or elementary bodies, yet no distinct evidence
had been obtained of their nature, until, in the year 1807, it
was furnished by the splendid discoveries of Sir H. Davy.
From the facts which have been stated in a former section
respecting the powers of electrical decomposition, it ap¬
peared to that philosopher a natural inference, that the same
powers, applied in a state of the highest possible intensity,
mi°*ht disunite the elements of some bodies, which had resisted
all other instruments of analysis. If potash, for example, were
an oxide, composed of oxygen united to an inflammable base,
it seemed to him probable, that when subjected to the action
of opposite electricities, the oxygen would be attracted by
the positive wire and repelled by the negative. At the same
* See Philosophical Magazine, xxxii. 18, 62.
SECT. I.
ANALYSIS OF FIXED ALKALIES.
217
time, the reverse process might be expected to take place
I with respect to the combustible base, the appearance of which
might be looked for at the negative pole.
In his first experiments, Sir H. Davy failed to effect the
decomposition of potash, owing to his employing the alkali in
i a state of aqueous solution, and to the consequent expenditure
i of the electrical energy in the mere decomposition of water.
In his next trials, the alkali whs liquefied by heat in a platinum
i dish, the outer surface of which, immediately under the alkali,
i wras connected with the zinc or positive end of a battery con¬
sisting of 100 pairs of plates, each six inches square. In this
state, the potash was touched with a platinum wire proceeding
from the copper or negative end of the battery ; when instantly
i a most intense light was exhibited at the negative wire, and a
: column of flame arose from the point of contact, evidently
c owing to the development of combustible matter. The results
c of the experiment could not, however, be collected, but were
: consumed immediately on being f rmed.
The chief difficulty in subjecting potash to electrical action
a is, that in a perfectly dry state it is a complete non-conductor
of electricity. When rendered, however, in the least degree
moist by breathing on it, it readily undergoes fusion and de-
f composition, by the application of strong electrical powers.
5 For this purpose, a piece of potash, weighing from 60 to 70
t grains, may be placed on a small insulated plate of platinum,
i and may be connected, in the wray already described, with the
opposite end of a powerful electrical battery, containing not
less than 100 pairs of six inch plates. On establishing the
: connection, the potash will fuse at both places where it is in
contact with the platinum. A violent effervescence will be seen
at the upper surface, arising, as Sir FI. Davy has ascertained,
from the escape of oxygen gas. At the lower or negative sur¬
face, no gas will be liberated ; blit small bubbles wall appear,
r having a high metallic lustre, and being precisely similar in
visible characters to quicksilver. Some of these globules burn
a with an explosion and bright flame ; wdiile others are merely
: tarnished, and are protected from farther change by a white
i film, which forms on their surface
* For the repetition of this experiment, very useful practical directions
may be found in a paper by Mr. Singer— Nicholson’s Journal, xxiv. 174.
cr
SI 8 ALKALIES. CHAP. VIII.
This production of metallic globules is entirely independent
of the action of the atmosphere; for Sir H. Davy finds that
they may be produced in vacuo .
Pure soda gives similar results; but its decomposition de¬
mands a greater intensity of action. The quantity of soda
should not exceed 15 or 20 grains ; and the distance between
the platina surfaces must be reduced from to ~ or -A of an
inch. The metal from soda does not, like that from potash,
continue fluid at the temperature of the atmosphere; but
speedily becomes solid, and bears a considerable resemblance
to silver. When the electrical power is much increased, glo¬
bules of the metal fly with great velocity through the air, in a
state of vivid combustion, producing beautiful jets of fire.
To preserve these new substances, it is necessary to im¬
merse them immediately in pure naphtha, a fluid which will
be described in a subsequent part of the work. If they are
exposed to the atmosphere, they are rapidly converted back
again into the state of pure potash or pure soda. To prevent
their oxidation still more effectually, Mr. Pepys has proposed
to produce them under naphtha; and has contrived an inge¬
nious apparatus for this purpose, which k described in the
51st volume of the Philosophical Magazine, page 241.
When the globules, obtained either from potash or soda,
are exposed to the action of air over mercury in graduated
glass tubes, an absorption of oxygen happens ; and a crust of
alkali is formed on the surface, which defends the interior
from farther change. When heat is applied to the globules
similarly confined, a rapid combustion ensues, attended with
a brilliant white flame. The globules are found, after the ex¬
periment, converted into a white substance ; which is potash
when we have used those from potash, and soda when the
globules from soda have been employed. In this process,
oxygen is absorbed, and the weight of the alkali produced is
found to exceed that of the globules consumed.
When either of these substances is thrown into wrater, a
rapid disengagement of hydrogen gas takes place; and the
oxygen of the water, uniting with the globules, regenerates
alkali.
Nothing then can be more satisfactory than the evidence,
furnished by these experiments, of the nature of the fixed
3 SECT. T.
ANALYSIS OF FIXED ALKALIES.
219
fl alkalies. By the powerful agency of opposite electricities, each
U of them is resolved into oxygen and a peculiar base*. This
: base, like other combustible bodies, is repelled by positively
f: electrified surfaces, and attracted by negative ones ; and hence
;t its own natural state of electricity must necessarily be positive.
/ Again, by uniting with oxygen, these bases are once more
[I changed into alkali, either slowly at ordinary temperatures ;
eJ or with heat and light, if their temperatures be raised. We
i have the evidence, therefore, both of analysis and synthesis,
f; that each of the fixed alkalies is a compound of oxygen with a
a peculiar inflammable basis.
But in what class of combustible bodies are we to arrange
[j the alkaline bases ? Some properties, common to both, have
i influenced Sir H. Davy to place them among the metals, with
u which they agree in opacity, lustre, malleability, conducting
q powers as to heat and electricity, and in their qualities of che¬
rt mical combination. The only property, which can be urged
f] against this arrangement, is their extreme levity, which even
q exceeds that of water. But when we compare the differences
7 which exist among the metals themselves, this will scarcely be
a considered as a .valid objection. Tellurium, for example,
7 which no chemist hesitates to consider as a metal, is only
6 about six times heavier than the base of soda, while it is four
i times lighter than platinum ; thus forming a sort of link be-
j tween the old metals and the bases of the alkalies.
In giving names to the alkaline bases, Sir IT. Davy has
5 adopted that termination, which, by common consent, has
f been applied to other newly discovered metals, and which,
t though originally Latin, is now naturalized in our language.
The base of potash he has called potassium, and the base of
i soda sodium ; and these names have met with universal ac-
i ceptation among chemical philosophers.
It is not, however, by electrical means only that the de¬
composition of the fixed alkalies has been accomplished. Soon
after Sir H. Davy’s discoveries were known at Paris, Messrs.
Gay Lussac and Thenardf succeeded in their attempts to
* The proportions of oxygen and base in each will be found at the end ot
the articles Potassium and Sodium.
f Annales de Chimie, Ixv. 325 ; or Memoires d’Arcueil, ii. 299.
220
ALKALIES.
CHAP. VIII.
decompose both the fixed alkalies, without the aid of a Voltaic
apparatus, and merely by the intervention of chemical affini¬
ties. Their process, though it affords the alkaline bases of
less purity, yields them in much larger quantity than the elec¬
trical analysis, viz. to the amount of nearly 400 grains by one
operation. It consists in bringing the alkalies into contact
with intensely heated iron, which, at this temperature, attracts
oxygen more strongly than the alkaline base retains it.
The apparatus, used for obtaining potassium, differs very
little from that which is commonly employed to decompose
water by means of iron It consists of a common gun-barrel
curved and drawn out, at one end, to rather a smaller dia¬
meter, as represented in the 9th plate, fig. 83, c. To one end
is adapted an iron tube a , of the capacity of two cubic inches,
for containing the potash. At the bottom of this tube is a
small hole, through which the potash gradually fiowrs. To
the opposite end of the gun-barrel a tube of safety e is to be
cemented ; and into this a sufficient quantity poured, either
of mercury or naphtha. Into the gun -barrel, 2 a parts of very
clean iron turnings are to be introduced, and pushed on to
the bent part c. The tube, carefully luted, is then to be
placed in a small furnace nine or ten inches in diameter, and
provided with a pair of double blast bellows, the pipe from
which is shown at f. The next step is to insert the tube a in
its place, after having put into it If parts of pure potash, de¬
prived of as much water as possible by previous fusion. The
■whole apparatus should be perfectly dry, clean, and impervi¬
ous to air.
A strong heat is now to be excited in the furnace d; and'
while this is doing, the tube containing the potash, as well as
the opposite end of the barrel, should be kept cool by ice.
When the barrel lias attained a white heat, the potash in a
* Hachette in Philosophical Magazine, xxxii. 89 ; and Mr. E. Davy,
ditto, page 276. Ample details respecting the preparation of potassium are,
also, given in the 1st vol. of Gay Lussac and Thenard’s Recherches Phy-
sico-Chimiques ; and a simple and ingenious apparatus, for procuring this
metal, is described by Mr. Tennant in the Phil. Trans, for 1814. See also
Mr. Branded directions in the Supplement now publishing to the Encyclop.
Britan, iii. 36.
SECT. I.
ANALYSTS OF FIXED ALKALIES.
221
: may be melted by a small portable furnace. It will then flow,
through the small hole, upon the iron turnings. A consider-
j able quantity of hydrogen gas will be evolved by the decompo¬
sition of that portion of water, which the potash retains even
I after fusion, and which has been shown to exceed 13 per cent .
i When the production of this gas slackens, we may remove
the small furnace from beneath the tube u, and increase the
heat in the furnace cL in order to restore to the iron turnings
o
at c the temperature proper for decomposing more potash.
| These operations may be repeated, alternately, till no more
5^ gas is produced ; but last of all, the heat in the furnape should
i be strongly, raised, in order to drive off some of the potassium.
which strongly adheres to the iron turnings.
When the furnace is quite cold, the safety tube e is to be
s) removed, and its place supplied by an iron plug. If the end
a of the gun-barrel, projecting from this side of the furnace, has
been kept carefully cooled during the experiment, the metal
will be found adhering to it, in the form of brilliant laminae,
d In order to extract it, the gun-barrel is to be cut at the com-
£ mencement of the part which has been kept cool, where the
| greatest quantity will be found. Another portion will be
• found close to the plug, and this adheres so slightly to the
i gun-barrel, that the least effort serves to detach it. It is even
M partly oxidized by the air, which gains access during the cool-
>:ing of the furnace; and when the whole is covered with naph-
; tha, the oxidized part is detached in laminae, exposing a white
riand brilliant metallic surface.
The potassium , which is condensed nearest the furnace, must
be detached by a sharp chisel, and in the largest pieces we
can possibly break off; for if it be in small molecules, it in¬
flames in the air, even at very low temperatures. In the mid¬
dle of the gun-barrel we shall find an amalgam of potassium
; and iron, which becomes green on exposure to the air, the
\ potassium returning to the state of potash.
When the iron turnings were very clean, the potash very
dry and pure, and the whole apparatus free from foreign
» matters, the metal produced differed very little from that ob¬
tained by a Voltaic battery. Its lustre, ductility, and malle¬
ability were similar. Its point of fusion and specific gra vity.
222
ALKALIES.
CHAP. VIII.
however, were a little higher; for it required nearly 130°
Fahrenheit, to render it perfectly fluid, and was to water as
796 to 1000 at 60° Fahrenheit. This Sir II. Davy ascribes
to contamination with a minute proportion of iron. The
affinities, indeed, by which the decomposition is produced,
he supposes to be those of iron for oxygen, of iron for pot¬
assium, and of potassium for hydrogen.
Charcoal, it has been asserted by Curaudau *, may be em¬
ployed, also, for the decomposition of the alkalies. To ensure
success in the process, great attention, it appears, is necessary
to the manipulations, which are fully described in the memoir
of the inventor. The fact sufficiently explains an observation
of Professor Woodhousef. A mixture of half a pound of
soot and two ounces of pearlash, was exposed for two hours
in a covered crucible to an intense heat. When the mixture
became cold it was emptied upon a plate, and a small quantity
of water poured upon it, when it immediately took fire. This j
could only be owing to the conversion of part of the potash j
into potassium.
Art. 3. — Potassium.
I. The base of potash, at 60° Fahrenheit, exists in small
globules, which possess the metallic lustre, opacity, and gene- ■
ral appearance of mercury ; so that when a globule of mercury i
is placed near one of potassium the eye can discover no differ¬
ence between them. At this temperature, however, the metal 1
Is only imperfectly fluid ; at 70° it becomes more fluid ; and I
at 150° its fluidity is so perfect, that several globules may
easily be made to run into one.
% reducing its temperature, potassium becomes, at 50° I
Fahrenheit, a soft and malleable solid, which has the lustre )
of polished silver. At about the freezing point of wrater, it ;
becomes hard and brittle, and exhibits, when broken, a crys- -s
taliized texture, which, in the microscope, seems composed
of beautiful facets of a perfect whiteness and high metallic
splendor.
* Nicholson’s Journal, xxiv. 37.
3
f Ibid. xxi. 290.
SECT. 1.
POTASSIUM.
£25
To be converted into vapour, it requires a temperature ap¬
proaching that of a red heat; and, when the experiment is
- conducted under proper circumstances, it is found unaltered
after distillation.
II. Potassium is a perfect conductor both of electricity and
of heat.
I •
III. Its specific gravity at 60° Fahrenheit, making some
allowance for unavoidable errors in the experiment, is as 6 to
10, the latter number being assumed as that of water. Gay
) Lussac and Thenard make it between 8 and 9, and Bucholz
8.76; but they probably operated on a less pure substance.
1 Even in its solid form, it swims in naphtha, whose specific
[ gravity is about 7-k to 10. The most recent statement of its
specific gravity, by Sir H. Davy, fixes it between 8 and 9.
IV. Its combustibility has already been noticed. At the
c3 temperature of the atmosphere, it absorbs oxygen slowly ; but
1 if heated nearly to redness, or to its point of vaporization, it
ii burns with a brilliant white flame and a very intense heat.
V. It appears to be susceptible of different degrees or stages
i of oxidizement. istly, By heating it to a point, below what
g is necessary for its inflammation, either in common air or
! oxygen gas; or, (which is still better) by confining it, for
some days, in an empty phial loosely corked, a substance is
formed of a bluish grey colour, softer than wax, and readily
fusible. This substance takes fire in oxygen gas, or even com-
i mon air, at about 70° Fahrenheit, and acts on water, giving
out hydrogen, but in less quantity than is extricated by pot¬
assium.
2. The second oxide is potash, which is most effectually
produced by the action of potassium on water.
3. Potassium, gently heated on a platinum tray in oxygen
; gas, gives, for the result of its combustion, an orange coloured
i fusible substance. It is necessary to protect the platinum from
its action, by dipping the tray, before the experiment, into
muriate of potash melted by heat. The precise nature of this
compound was first explained, and its properties examined, by
Gay Lussac and Thenard. It is fusible at a lower heat than
5 hydrate of potash, and crystallizes in laminae by cooling.
J When thrown into water, oxygen gas is evolved, and the
22l<
ALKALIES.
chap. viii.
substance passes, by this loss of oxygen, to the state of potash.
Oxygen gas is, also, separated, by heating it strongly on a pla¬
tinum tray coated with muriate of potash ; and a grey vitreous
substance remains, which Sir H. Davy considers as absolutely
pure potash. Almost all bodies, that have an attraction for
oxygen, decompose this orange oxide, and reduce it to the
state of potash, which, in some cases, combines with the new
compound. Charcoal, for example, with the excess of oxy¬
gen in the orange substance, forms carbonic acid; and this
acid, uniting with the potash that is produced, composes car¬
bonate of potash.
VI. The action of potassium on water is attended with some
beautiful phenomena. When it is thrown upon water exposed
to the atmosphere, or when it is brought into contact with a
drop of water, it decomposes the water with great violence;
an instantaneous explosion is produced with a vehement flame;
and a solution of pure potash is the result. The hydrogen
gas, which is disengaged, appears to dissolve a portion of pot¬
assium ; for, on escaping into the air, it forms a white ring of
smoke, gradually enlarging as it ascends, like the phosphureted
hydrogen gas.
When water is made to act on the base of potash, atmo--:
spheric air being excluded, there is much heat and noise, but:
no luminous appearance; and the gas evolved is pure hydro- A
gen. It is of importance to remember that each grain of pot-
assiuin, by acting on water, detaches about 1.06 cubic inch til
of hydrogen gas.
If a globule of the base of potash be placed on ice, it in¬
stantly burns with a bright flame, and a deep hole is made in i
the ice filled with a fluid which is found to be a solution of <
potash.
The production of alkali, by the action of water on potas- ;
sium, is most satisfactorily shown, by dropping a globule of fJ
the metal upon moistened paper, which has been tinged with 1
turmeric. At the moment when the globule comes into con- si
tact with the paper, it burns, and moves rapidly as if in : I
search of moisture, leaving behind it a deep reddish brown
trace, and acting upon the paper exactly like dry caustic
potash.
SECT. 3.
POTASSIUM.
225
So strong, indeed, is the affinity of potassium for oxygen,
that it discovers and decomposes the small quantities of
water contained in alcohol and ether, even when carefully
purified, and disengages, from both these fluids, hydrogen
gas.
On naphtha colourless and recently distilled, potassium has
very little power of action; but in naphtha, which has been
exposed to the air, it soon oxidates, and alkali is formed,
which unites with the naphtha into a brown soap, that collects
round the globules.
VII. When thrown into the liquid mineral acid, the base
of potash inflames, and burns on the surface; or, if kept be-
: neath the surface, its effects are such as may be explained by
Jits affinity for oxygen. In concentrated sulphuric acid, a
white saline substance is formed, which is probably concern-
!trated sulphuric acid surrounded by sulphur. At the same
time a gas escapes which has the smell of sulphurous acid
mixed with hydrogen gas. In nitrous acid, nitrous gas is
| disengaged, and nitrate of potash formed. In cxymuriatic
acid gas, it burns vividly with bright scintillations, and niuri-
; ate of potash is generated.
VIII. Potassium readily combines with the simple com¬
bustibles. To unite it with sulphur or phosphorus, it must
be melted with these bodies under naphtha.
The phosphuret of potassium requires for its fusion a stronger
heat than either of its constituents. It is of the colour of
lead ; and, when spread out, has a lustre similar to polished
lead. By exposure to the air, or by rapid combustion, it
forms phosphate of potash. Besides this, there is, also, a
chocolate coloured compound of potassium and phosphorus;
so that it is probable these two bodies unite in different pro¬
portions, the lead coloured compound consisting of 2 atoms
of metal + 1 of phosphorus ; and the chocolate of 1 atom of
metal + 1 of phosphorus.
When potassium is fused with sulphur, in a vessel filled
with the vapour of naphtha, a rapid combination ensues, ae-
d companied with heat and light, and a disengagement of sul-
phureted hydrogen. The result is a grey substance not unlike
VOL. i. <2
226
ALKALIES.
CHAP. VIII.
artificial sulphuret of iron. Its formation and properties have
been investigated by VauqueliiU.
IX. With mercury, potassium gives some extraordinary
and beautiful results. The combination is very rapid, and
is effected by merely bringing them into contact at the tem¬
perature of the atmosphere. The amalgam, in which the
potassium is in least proportion, seems to consist of about 1
part in weight of basis and 70 of mercury. It is very soft%
and malleable ; but by increasing the proportion of potassium,
we augment, in a proportional degree, the solidity and brit¬
tleness of the compound.
The compound of mercury and potassium may be ob¬
tained by an easy and simple process, first pointed out by
Berzelius. Mercury, to the depth of a line, is put into a
glass capsule, two inches in diameter, with a flat bottom.
On this a solution of pure potash is poured; an iron wire
connects the mercury with the negative pole of a galvanic
arrangement, which needs not contain more than 20 pairs of
plates ; and a spiral platina wire, from the positive pole, is
immersed in the solution, and kept within about a line from
the surface of the mercury. In six hours, the effect is ob¬
servable, and in 24? is very distinct : for, in that time, more
than 1200 grains of mercury will be rendered solid by combi¬
nation with potassium. Unfortunately, this combination can¬
not be so decomposed, as to obtain the potassium in a separate i t
state.
In this state of division, potassium appears to have its affi- *f|
nity for oxygen considerably increased. By a few minutes’ s
exposure to the air, potash is formed which deliquiates, and
the mercury is left pure and unaltered. When a globule is 5 ;
thrown into water, it produces a rapid decomposition and a i ;
hissing noise ; potash is formed ; pure hydrogen disengaged;
and the mercury remains free.
The fluid amalgam of potassium and mercury dissolves all .
the metals ; and in this state of union, mercury even acquires
the power of acting on platina.
* Ann de Chiin. et. PI13 S. vi. 22.
I
SECT. I.
POTASSIUM.
227
Potassium unites, also, with gold, silver, and copper; and,
when the compounds are thrown into water, this fluid is de-
; composed, potash is formed, and the metals are separated un¬
altered. When the reduction of an ore has been accom¬
plished by the use of fluxes containing potash, M. Vauquelin
has shown that the revived metal contains a greater or less
proportion of potash, which modifies its properties. By ex¬
posure to the air, or by the action of water, this impurity may
be removed
X. Potassium reduces all the metallic oxides when heated
i with them, even of those metals which most powerfully attract
oxygen, such as oxides of iron. In consequence of this pro¬
perty it decomposes and corrodes flint and green glass by a
very gentle heat ; potash is generated with the oxygen taken
i from the metal, which dissolves the glass and exposes a new
surface. At a red heat even the purest glass, formed merely
i of potash and silex, is acted upon. The alkali in the glass
seems to give up a part of its oxygen to the potassium, and
an oxide of potassium results, with a less proportion of oxy¬
gen than is necessary to constitute potash. The silex, also,
; it is probable, is partly de-oxidized.
From this summary of the action of potassium, it appears
that all the most remarkable effects which it exhibits, are con¬
nected with its affinity for oxygen, which is sufficiently ener¬
getic to enable it to take oxygen from all other bodies. Hence
the application of potassium to any substance is the best test
of its containing oxygen, which, if present, it cannot fail to
> detect.
It was important to determine the proportions in which
potassium and oxygen combine, when potash is regenerated.
This Sir H. Davy investigated by two different processes.
The one consisted in ascertaining how much oxygen gas dis¬
appears by the action of a given quantity of potassium ; the
other how much hydrogen is disengaged from water by a
known weight of the same substance. Dividing the bulk of
the hydrogen gas by 2, he learned the quantity of oxygen
which had been taken from the water.
* Ann. de Chim. et Phys. vii. 32.
228
ALKALIES.
CHAP. VIII.
The coincidence of results, obtained by these different
methods, is remarkable. By the action of potassium on oxy¬
gen gas, it appeared, on an average, that
o , i • , c C 86.1 potassium.
Potash consists oi < 1 J
C 13.9 oxygen.
100.
By the agency of water, the proportions differed only by a
small fraction, so that we may state in round numbers that the
base is to the oxygen as six to one, or that
Potash is composed of -f 80 hotass^ulTb
L 14 oxygen.
100.
Subsequent experiments, however, have made some change
necessary in these numbers. Gay Lussac and Thenard found,
that 100 parts by weight of potassium take 19.945 of oxygen
from water ; and Sir II. Davy, by the action of 8 grains of 1
potassium on water, obtained, on an average, .9^- cubic inches
of hydrogen gas, showing that 4-| cubic inches, ( = 1.61 grains) 0
of oxygen had combined with the metal. Berzelius investi- -
gated the composition of potash, by exposing an amalgam of
potassium and mercury, containing known proportions of
those metals, to water; saturating the potash with muriatic
acid ; and determining its weight by the muriate of potash
formed*. The following table shows the proportions of
potassium and oxygen in 100 grains of potash, as deduced
from these different authorities. One hundred grains of pot¬
ash contain,
Potassium.
According to Sir H. Davy . 83.2
— - — — — Gay Lussac . 83.37
— - — — Berzelius . 82.97
Oxygen.
16.8
16.63
17.03
If deduced from the atomic theory, the true proportions
should be 85 of potassium to 15 oxygen, numbers very near
those originally obtained by Sir H. Davy. It is probable,
indeed, that sources of inaccuracy may exist in the experi-
* 80 Ann. de Chim. 245.
1 SECT. I. POTASSIUM. 229
ments, sufficient to account for this small deviation from
; theory ; and that potash is a compound of 1 atom of potas-
■ sium weighing 42.5 with 1 atom of oxygen weighing 7.5.
I Hence the weight of the atom of potash will be 50 ; and an
atom of water (8.5) being added, the atom of hydrate of pot-
i ash will weigh 58.5.
It is doubtful whether the grey compound (mentioned in
§ v.) be a true sub-oxide of potassium , or merely a mixture of
potash with potassium. If the former, it must consist of two
i atoms of potassium (85) with one atom of oxygen (7.5) =
i 92.5. But the latter view of its nature is the most probable one.
The composition of the orange oxide cannot be assigned,
j from the quantity of oxygen, absorbed in the experiments, by
I which it is produced ; for in eight results, obtained by Gay
! Lussac and Thenard, there is not a sufficient agreement to
decide this point. It seems probable that the oxygen, which
: converts potassium into this substance, is twice that which
>i converts it into potash ; and that the orange oxide consists of
1 atom of potassium = 42.5, + 2 atoms of oxygen = 15,
i which would make the weight of the atom of orange oxide
j 57.5.
Potassureted Hydrogen Gas .
This name I would propose for the solution of potassium in
i hydrogen gas, which, it has already been stated, results from
l the action of potassium on water, and, as appears from Sir
H. Davy’s experiments, may be formed, directly, by heating
the metal in hydrogen gas. A large portion of potassium is
i thus dissolved; but the greater part precipitates on cooling.
This gas is spontaneously inflammable in the atmosphere;
< burns with a very brilliant light, which is purple at the edges ;
and throws off dense vapours of potash. It loses its inflam-
i inability by keeping; is heavier than hydrogen gas; and is
very dilatable by electricity. Besides the gas, which is spon-
i taneously combustible, there is also, according to Sementini,
another compound of potassium and hydrogen, which is not
i possessed of this property, and probably contains a less pro-
i portion of the combustible metal.
Gay Lussac and Thenard # have succeeded, also, in form-
* Recherches, i. 176.
230
ALKALIES.
CHAP. VII I.
ing a solid compound of potassium and hydrogen. The
process consists in heating the metal in hydrogen gas ; and
the only difficulty is to regulate the heat, for a high tempe¬
rature decomposes the compound. The flame of a spirit
lamp, applied to potassium, in a retort filled with hydrogen
gas, occasions an absorption of the gas, and the formation of
a solid hydruret of potassium.
The colour of this substance is grey; it is destitute of me¬
tallic lustre ; and is infusible. It is not inflammable, either in
air or in oxygen gas at common temperatures, but burns vi¬
vidly at a high one. When strongly heated in a close vessel,
it is totally decomposed ; all the hydrogen it contains is libe¬
rated in the state of gas ; and the potassium remains. When
brought into contact with heated mercury, hydrogen gas is
evolved, and an amalgam of potassium and mercury is pro¬
duced.
Nitrogen gas has not, at any temperature, any action on
potassium.
Art. 4.- — Sodium.
The base of soda agrees, in many of its properties, with the *
base of potash, and exerts on several bodies a similar action, , :i
with the obvious exception that the results are compounds if;
of soda instead of potash. Thus with nitric acid it affords «
nitrate of soda; with oxy- muriatic acid, muriate of soda. In 1
this place, therefore, I shall describe only such of its pro- - h
perties as are peculiar to and characteristic of it.
I. Sodium, at common temperatures, exists in a solid form, i
It is white, opaque ; and, when examined under a thin film
of naphtha, has the lustre and general appearance of silver.
It is exceedingly malleable, and much softer than any of the . i
common metallic substances. When pressed upon byapla-4
tinum blade with a small force, it spreads into thin leaves ; -
and a globule of or T’¥th of an inch in diameter is easily
spread over a surface of a quarter of an inch. This property I
is not diminished, by cooling it to 32° Fahrenheit. Several
globules, also, may, by strong pressure, be forced into one ;
so that the property of weldings which belongs to platinum and r
SECT. I
SODIUM
231
iron at a high degree of heat only, is possessed by this sub-
; stance at common temperatures.
II. It is lighter than water. As near as can be determined,
i its specific gravity is as 0.9348 to 1.
III. It is much less fusible than the base of potash. At
120° Fahrenheit, it begins to lose its cohesion, and it is a
perfect fluid at about 180°. Hence it readily fuses under
> heated naphtha.
IV. Its point of vaporization has not been ascertained ; but
i it remains fixed, in a state of ignition, at the point of fusion of
j plate glass.
V. When sodium is exposed to the atmosphere, it imme-
i diately tarnishes, and by degrees becomes covered with a
i white crust of soda, which deliquiates more slowly than that
1 formed on potassium.
VI. It combines with oxygen, slowly and without luminous
3 appearance, at all common temperatures. When heated, the
] combination becomes more rapid ; but no light is emitted till
i it becomes nearly red hot. The flame, which it then pro-
i duces, is white, and it sends forth bright sparks, exhibiting a
i very beautiful effect. In common air, it burns with a similar
d colour to charcoal, but of much greater splendour.
VII. When thrown into water, it produces a violent offer-
i vescence and a loud hissing noise ; it combines with the oxy-
] gen of the water to form soda ; and hydrogen gas is evolved,
i which does not, however, as in the case of potassium, hold
3 any of the alkaline base in solution. Neither can sodium be
[j made to dissolve in hydrogen gas, by being heated in contact
When thrown into hot water, the decomposition is more
violent, and in this case a few scintillations are generally ob¬
served at the surface of the fluid ; but this is owing to small
particles of the base, which are ejected from the w'ater, suffi¬
ciently heated to burn in passing through the atmosphere.
VIII. Its action on alcohol, ether, volatile oils, and acids,
; is similar to that of potassium; but with nitric acid a vivid in¬
flammation is produced.
IX. Sodium appears to be susceptible of different degrees
of oxydation. 1st. When it is fused with dry soda, a parti-
5
232
ALKALIES.
CHAP. VIII.
tion of oxygen takes place between the alkali and the metal.
A deep brown fluid is produced, which becomes a dark grey
solid on cooling. This substance is capable of attracting
oxygen from the atmosphere, and of decomposing water, by
which it is again converted into soda. The same oxide of
sodium is formed, by fusing this metal in tubes of plate glass.
It is of a greyish colour, destitute of lustre, brittle, and
gives hydrogen when acted on by water, but less than an equal
weight of sodium. It may, however, be doubted, whether this
is a compound of sodium and oxygen, or merely a mixture of
the metal with soda.
2d, The second oxide of sodium (or first, if the one which
has been just described be only a mechanical mixture) is soda.
It may be formed by burning sodium, in a quantity of air con¬
taining just oxygen enough to convert the metal into alkali. It
is of a grey colour ; of a vitreous fracture ; and requires a strong
red heat for its fusion. Water is absorbed by it with violence,
and converts it into hydrate of soda.
3d. The orange oxide of sodium may be formed, by burn¬
ing the metal with an excess of oxygen. It is of a deep orange
colour, very fusible, and a non-conductor of electricity. When
acted on by water, its excess of oxygen escapes, and it becomes
soda. It deflagrates with most combustible bodies.
X. There is scarcely any difference between the visible phe¬
nomena attending the action of the base of soda, and that of
potash on sulphur, phosphorus, and the metals. The sul-
phuret of sodium has a deep grey colour ; the phosphuret re¬
sembles lead. Added to mercury in the proportion of TVth,
it renders that metal a fixed solid of the colour of silver, and
the combination is attended with a considerable degree of heat.
This amalgam seems, like that of potassium, to form triple
compounds with other metals, and even with iron and platinum,
which remain united with the mercury, when it is deprived of
the new metal by the action of air.
The proportions, in which this base unites with oxygen to
form soda, were investigated by the methods already described
in the article Potassium. The results of Sir H. Davy ; of Gay
Lussac and Thenard ; and of Berzelius, are given in the fol¬
lowing table:
SECT. II.
LITIIIA OR LITHINA.
233
Per Davy (1807) 100 soda contain
— Ditto»(181 1 ) .
— Gay Lussac .
— Berzelius * . . . . .
Sodium.
Oxygen.
22.3
25.4
25,37
27.71
The proportions that would best accord with the atomic
theory, are 77.5 of sodium to 22.5 of oxygen; for this last
number agrees with the weight of three atoms of oxygen. And
on the supposition that soda is a compound of 1 atom of so-
> dium x 1 atom of oxygen, by dividing 77.5 by 3 we should
i obtain the weight of the atom of sodium, viz. 25.8. In this
case the atom of soda would weigh 33.3, and the atom of hy¬
drate ol soda 41.8. The number, assumed by Dr. Wollaston
to represent sodium, (oxygen being 10) is 29.1 ; and soda will,
i therefore, be denoted, on his scale, by 29.1 x 1 0 — 39.1.
The peroxide Dr. Thomson is disposed to consider as a com¬
pound of two atoms of sodium with three atoms of oxygen f .
SECTION II.
Lithia or Lithina .
The discovery of this new substance, which dates only from
the commencement of the present year, is due to the skill and
sagacity of M. Arfvredson, a pupil of Berzelius. In the ana-
l}Tsis of a mineral called Petalite , (first distinguished as a new
species by M. D’ Andrada, who found it in the mine of Uto, in
Sweden,) about 3 per cent, of an alkali was obtained, which
M. Arfvredson at first supposed to be soda. On more ac¬
curate examination, however, the new substance displayed pro¬
perties, entirely distinct from those of either soda or potash,
especially in possessing the power of neutralizing a much greater
quantity of the different acids than either of those alkalies ;
in which respect it even surpassed magnesia. To distinguish
it from the two other fixed alkalies, both of vegetable origin,
it received the name of lithion ; and this term, to suit the ana-
* 80 Ann. de Chim. 251.
f Ann. of Phil. x. 100.
234
LITHIA OR LITHINA.
CHAP. vm»
logy of the other alkalies, was afterwards converted into
lithia or lithina.
The proportion of lithina in petalite has since been found
to be 5 per cent. ; and from some very pure pieces of that mi¬
neral, Vauquelin has extracted even 7 per cent. M. Arf-
vredson has discovered it, to the amount of 8 per cent, in
triphane or spodumene , a mineral which is not so scarce as pe¬
talite ; and, to the extent of 4 per cent, in crystallized lepido -
lite. The process employed by him has not been described ;
but it probably consisted in fusing the mineral wTith twice or
three times its weight of potash ; dissolving the fused mass in
muriatic acid; evaporating to dryness; and digesting in al¬
cohol, which takes up scarcely any thing but a compound of
the new earth with muriatic acid. By evaporating a second
time to dryness, and again dissolving in alcohol, the muriate
of lithina is obtained pure. Vauquelin extracted it from pe¬
talite by the intervention of nitrate of barytes, employed,
probably, in the manner which will be described in the chap¬
ter on the analysis of minerals.
The muriate of lithina may be decomposed by digestion
with carbonate of silver ; and the solution of the carbonate,
being decomposed by lime or by barytes, yields a solution of
pure lithina, which may be evaporated to dryness out of
contact with the air, from which it rapidly imbibes carbonic
acid.
Pure lithina is very soluble in water, and, like the other
alkalies, has an acrid, caustic taste. Like them also, it changes
vegetable blue colours to green. When heated in contact
with platinum, it fuses, and then acts on the metal. That it
agrees with the other alkalies in containing a metallic base,
has been proved by Sir H. Davy, who applied the power of
a galvanic battery to a portion of the carbonate, fused in a
platinum capsule. On rendering the platinum positive, and
bringing a negative wire to the surface of the fused carbonate,
the alkali was decomposed wuth bright scintillations ; but the
reduced metal burned again so rapidly, that it was only ob¬
served to be of a white colour and very similar to sodium.
From analogy, it has received the name of lithium. The pro¬
portion, in which this metal unites w ith oxygen, has, of course,
SECT. II.
LITHIA OR LITHINA.
235
not been determined by direct experiment ; but it has been
deduced by Vauquelin, from an analysis of the sulphate of
lithina, and the application of the law that the proportion be¬
tween the oxygen of sulphuric acid, and that of the bases
which it saturates, is as 3 to 1", to be as follows:
Lithium . 56.50 . 100 ...... 130
Oxygen ...... 43.50 . 77 . . 100
100.
It would be premature, in the present imperfect state of our
knowledge of this new metal and alkali, to determine their
equivalents, or in other words, the weights of their atoms.
Instead, also, of describing the compounds of lithina, like
those of the other alkalies, in future parts of the work, I shall
state, in this place, the little that is known respecting them.
With sulphur , lithina affords a yellow, and very soluble
compound, which is decomposed by acids, with the same phe¬
nomena as the alkaline sulphurets, and, from the abundance
of the precipitate, appears to contain a large proportion of
sulphur.
Sulphate of lithina crystallizes in small prisms of a shining
white colour. It is more fusible and soluble than sulphate of
potash, and has a saline, not a bitter, taste. It is constituted of
Sulphuric acid . 69.20
Lithina . 31.80
100.
The muriate and the nitrate of lithina are both deliquescent
salts. The carbonate is efflorescent in the air, and is sparingly
soluble, requiring about 100 times its weight of cold water.
The solution effervesces with acids ; changes vegetable blue
colours to green ; decomposes solutions of alumine and mag¬
nesia, and of the metals ; disengages ammoniac from its com¬
binations ; and does not precipitate the muriate of platinum.
The dry carbonate, when fused on platinum, acts as powerfully
on that metal as the alkaline nitrates. The tartrate of lithina
is an efflorescent salt ; and the acetate , when evaporated, as¬
sumes the consistence of gum or syrup *.
* See Thomson’s Annals, xi. 291, 373, 447 ; xii. 15 ; Ann. de China. et
Phys. vii. 284, 313 ; and Journal of Science, &c. v. 337.
236
AMMONIA.
CHAP. Till.
SECTION III.
Pure Ammonia .
Art. 1. — Preparation and Qualities of Ammonia.
I. Ammonia, in its purest form, exists in the state of a gas.
In order to procure it, one of the following processes may be
employed.
(a) Mix together equal parts of muriate of ammonia and
dry quicklime, each separately powdered ; and introduce them
into a small gas bottle or retort. Apply the heat of a lamp;
and receive the gas, that is liberated, over mercury.
( b ) To a saturated solution of ammonia in water or the pure
liquid ammonia, in a gas bottle, apply the heat of a lamp ;
and collect the gas, as in a.
II. This gas lias the following properties :
(a) It has a strong and very pungent smell.
(5) It immediately extinguishes flame ; and is fatal to ani¬
mals. Before, however, a candle is extinguished, by immer¬
sion in this gas, the flame is enlarged, by the addition of ano¬
ther, of a pale yellow colour, which descends from the mouth
to the bottom of the jar. If the flame of the candle be only
in part immersed in the g as, this yellowish flame rises a few
lines above the other.
(c) It is lighter than atmospheric air. Hence a jar filled
with this gas, and placed with its mouth upwards, is soon
found to exchange its contents for common air, which, being
heavier, descends, and displaces the ammoniacal gas. By the
recent experiments of Messrs. Allen and Pcpys *, undertaken
at the desire of Sir H. Davy, 100 cubic inches of ammonia
weigh 18.18 grains, barometer 30, thermometer 60°. Ac¬
cording to Gay Lussac, its specific gravity is to that of com¬
mon air as 0.5967 to 10 ; and hence (taking 100 cubic inches
of air at 30.5 grains) 100 cubic inches of ammonia weigh
18.17 grains. Mr. Dalton assumes, that at a mean tempera¬
ture and pressure, ] 00 cubic inches weigh 18.6 grains; and
hence that its specific gravity is 6, air being 10. It does not
appear that in any of these trials, the gas was artificially dried.
* Philosophical Transactions, 1808, page 39.
SECT. III.
AMMONIA®
237
To effect its desiccation, potash or quicklime are best adapted ;
for dry muriate or chloride of lime, as well as several other
chlorides, absorb it rapidly *.
(d) Ammoniacal gas is not sufficiently inflammable to burn
when in contact with common air. But, when expelled from
the extremity of a pipe, having a small aperture surrounded by
oxygen gas, it may be kindled, and it then burns with a pale
yellow flame, the products of its combustion being water and
nitrogen gas.
(■ e ) Ammoniacal gas may be decomposed by transmitting it
through a red hot porcelain tube, which should be either well
glazed internally, or covered externally with a lute. It has
been ascertained by Thenard f, that when any of the five fol¬
lowing metals are enclosed in the tube, they promote the de¬
composition of ammonia in the order set down, viz. iron, cop¬
per, silver, gold, and platinum : iron being most effectual, and
platinum least. Iron, after the process, is found to be rendered
brittle, and copper still more so. The gas obtained always
i consists of 3 parts hydrogen by measure, and 1 nitrogen. None
of the metals is either increased or diminished in weight ; and
they can only, therefore, act as conductors of heat. Yet it is
singular that iron decomposes a much larger quantity than
platinum, and at a lower temperature.
( f ) It has been asserted by Guyton, that ammoniacal gas is
reduced to a liquid state at 70° below 0 of Fahrenheit ; but it
may be questioned whether the drops of liquid, which he ob¬
served, were any thing more than the watery vapour, which
the gas always contains, condensed by the cold, and saturated
with ammonia.
(g) Ammonia is rapidly absorbed by water. A drop or
two of water being admitted to a jar of this gas, confined over
mercury, the gas will be immediately absorbed, and the mer¬
cury will rise, so as to fill the whole of the jar, provided the gas
be sufficiently pure. Ice produces the same effect, in a still-
more remarkable manner. From Sir H. Davy’s experiments,
it appears that 100 grains of water absorb 3 4> grains of ammo-
niacal gas, or 190 cubic inches. Therefore a cubic inch of
* Journal of Science, v. 74.
f 85 Ann. de Chira. 61.
238
AMMONIA.
CHAP. VI 11.
water takes up 475 cubic inches of the gas. More recently
he has stated that at 50° Fahrenheit, water absorbs 670 times
its bulk, and acquires the specific gravity .875 *,
Alcohol, also, absorbs several times its bulk, and affords a
solution of ammonia in alcohol, which possesses the strong
smell, and other properties, of the gas.
(h) Water, by saturation with this gas, acquires its peculiar
smell ; and constitutes what has been called liquid ammonia ;
or, more properly, solution of pure ammonia in water. The
method of effecting this impregnation will be described here¬
after ; and processes will be given for obtaining the solution of
ammonia in considerable quantity, which cannot conveniently
be accomplished by the method described in experiment e.
This solution again yields its gas on applying heat. (See I. b.)
The strength of a solution of ammonia is influenced by two
circumstances, the temperature of the liquid, and the pressure
on its surface, for ammonia is not retained in water without
external force. The intervals of temperature, required to dou¬
ble the force of ammoniacal vapour, were ascertained by Mr.
Dalton to increase in ascending. When mixed with common
air, its elasticity is not altered; thus when ammoniacal gas of
15 inches force is mixed with a given volume of air, the air
is doubled in bulk.
Solutions of ammonia, when mixed with water, were found
by Sir FI. Davy, not to be sensibly condensed ; and, there¬
fore, if the quantity of ammonia in a solution of given specific
gravity be determined, it is easy to calculate the quantity in
solutions of other densities. The two following Tables, it may
be observed, do not exactly agree in their results, the quan¬
tity of ammonia, in solutions of the same density, being from
15 to 20 per cent, less in Mr. Dalton’s Table than in Sir FL
Davy’s. The numbers in the latter, marked with an asterisk,
were found by experiment, and from these the others were de-
d need.
* Elements of Chem. Phil. p. 263,
SECT. III.
AMMONIA.
239
Sir H. Davy’s Table of the Quantities of Ammoniacal Gas in
Solutions of different Densities (Temp. 50° Fahrenheit’s
Barometer, 29.8).
100 parts of
Specific
Gravity.
Of Ammonia.
100 parts of
Specific
Gravity.
Of Ammonia.
.8750*
32.5
.9435
14.53
.8875
29.25
.9476
13.46
.9000
G
26.
.9513
G
12.40
.9054*
• f— s
-4->
25.37
.9545
• rH
o3
11.56
.9166
G
o
22.07
.9573
G
o
10.82
.9255
o
19.54
.9597
o
10.17
.9326
17.52
.9619
9.60
.9385
15.88
.9692*
9,50
Mr. Dalton’s Table of the Quantities of Ammonia in Solutions
of different specific Gravities .
Specific
Gravity.
Grains of Am¬
monia in 100
water-grain
measures of
liquid.
Grains of Am¬
monia in 100
grains of
liquid.
Boiling point
of the liquid
in degrees of
Fahrenheit.
Volumes of
gas condensed
in a given
volume of
liquid.
850
30
35.3
26°
494
860
28
32.6
38°
456
870
26
29.9
50°
419
880
24
27.3
62°
382
890
22
24.7
74°
346
900
20
22.2
86°
31 J
910
18
19.8
98°
277
920
16
17.4
110°
244
930
14
15.1
122°
211
940
12
12.8
134°
180
950
10
10.5
146°
147
960
8
8.3
158°
116
970
6
6.2
173°
87
980
4
4.1
187°
57
990
2
2.
196°
28
ANALYSIS OF AMMONIA.
CHAP. VIII.
240
Art. 2. — Electrical Analysis of Ammonia,
(l) Ammoniacal gas is decomposed by electricity. Into a
glass tube, haying a conductor sealed hermetically into one
end (fig. 29), and standing inverted over mercury, pass about
one tenth of a cubic inch of ammoniacal gas; and transmit
through it a succession of electrical discharges from a Leyden
jar. The arrangement of the apparatus, for this purpose, is
shown in fig. 84, pi. ix. and is described in chap. v. sect. 1.
When two or three hundred discharges have been passed, the
gas will be found to have increased to almost twice its original
bulk, and to have lost its property of being absorbed by water.
Mix it with a quantity of oxygen gas, equal to between one
third and one half of its bulk, and pass an electric spark
through the mixture. An explosion will immediately happen;
and the quantity of gas will be considerably diminished. Note
the amount of the diminution by firing ; divide it by 3 ; and
multiply the product by 2. The result shows the quantity of
hydrogen gas in the mixed gases which have been generated
by electricity ; for two measures of hydrogen are saturated by i
one of oxygen gas.
Suppose, for example, that we expand 10 measures of am¬
monia to 18; and that, after adding 8 measures of oxygen
gas, we find the whole (= 26 measures) reduced by firing to
6 measures; the diminution will be 20. Dividing 20 by 3
we have 6.66, which multipled by 2 gives 13.32 measures of
hydrogen gas from 10 of ammonia. Deducting 13.32 from
18, we have 4.68 for the nitrogen gas contained in the pro¬
duct of electrization. Therefore 10 measures of ammonia
have been destroyed, and expanded into
13.32 measures of hydrogen gas,
4.68 - — - - — nitrogen gas.
According to the above proportions, 100 cubic inches of
ammonia, which weigh about 18 grains, if they could be de¬
composed by electricity, would give about 133 cubic inches of
hydrogen weighing 3.5 grains, and 46 of nitrogen weighing
14.4 grains, in all 17.9 grains, or one tenth of a grain less
than the ammonia decomposed. Mr. Dalton obtained 185
6
:| SECT. III.
ANALYSIS OF AMMONIA.
£41
(
measures of gas by decomposing 100 measures of ammonia;
i and, by comparing the products with the original gas, be finds
that the weight of the former rather exceeds that of the latter;
thus,
Grains.
100 measures of ammonia x sp. gr. .6 ----- 60
a
51.8-piitrogen, which x sp.gr. .967 = 50.09
133.2 hydrogen, which x sp.gr. .08 = 10.65
60.74
The excess of -f-ths of a grain in 60 he considers as too small
to affect the conclusion, and as arising from unavoidable in¬
accuracies in some of the data.
It is contended by Gay Lussac and Thenard, and the pro¬
bable accuracy of their result is admitted by Sir IT. Davy *
and by Dr. Wollaston, that 200 measures of ammonia are
resolvable, by analysis, into 300 of hydrogen and 100 of ni¬
trogen. This proportion is consistent with the theory of com¬
bination in definite volumes. There is, however, consider¬
able difficulty in ascertaining the precise amount of the gases
evolved from ammonia; for if either the gas itself, or the
mercury wdiich confines it, contain any moisture, the product
of gas, resulting from its decomposition, will exceed what it
ought to be. The problem is one of great importance to the
atomic theory, because from the proportion of the elements of
ammonia, is deduced the weight of the atom of nitrogen.
] This will differ considerably, according to the statement,
\ which we may adopt, of the amount of gases obtained by de-
) composing ammonia; their proportion to each other; and the
exact specific gravities of hydrogen and nitrogen gases. From
the data supplied by Mr. Dalton, it appears reasonable to
believe that the weight of nitrogen in ammonia is to that of
hydrogen nearly as 5 to 1, and the atom of nitrogen will, there¬
fore, be represented by 5, and that of ammonia by 5 + 1 =6.
On the scale of Dr. Wollaston, nitrogen is represented by 1 7.54;
which, with 3 proportions of hydrogen (1.32 X 3 = 3.9 6),
gives 21.5 for the equivalent of ammonia.
VOL. i.
* Elements of Chem, Phil. p. 269.
R
ANALYSIS OF AMMONIA.
CHAP. VIII.
(2) In the Philosophical Transactions for 1809, I have de¬
scribed a property of ammonia, which forms the basis of a
very easy and quick mode of analyzing that alkali. When
mingled with oxygen gas it may be inflamed by the electric
spark, precisely like a mixture of hydrogen and oxygen gases.
To obtain accurate results, however, it is necessary to use less
oxygen at first, than is sufficient to saturate the whole hydro¬
gen of the alkali. This is easily calculated. If, for example,
we take 10 measures of ammonia, we must use less oxygen
than will saturate 13 or 14 measures of hydrogen gas, the
quantity which exists in 10 of ammonia; and which require
about 7 of oxygen gas. It will be adviseable, therefore, not
to add above 4 or 5 of oxygen. The whole (suppose 15) will
probably, after firing, be reduced to about 9. To the re- -
maining gas admit 4 or 5 measures more of oxygen ; and on
passing the electric spark again, a second explosion will hap¬
pen, with a diminution of about 6 measures. But, in the
first explosion, the whole of the oxygen disappears, and it
must therefore have saturated a quantity of hydrogen equal to
10 measures; besides which, two thirds of the second dimi¬
nution (6-f-3 x 2) =4 measures are owing to the condensa¬
tion of hydrogen. Hence the whole hydrogen is 10 + 4 = 14.
The nitrogen, the whole of which exists in the product of
the first detonation, is ascertained by deducting from it (viz,1
from 9 in the present instance) the second quantity of hydro¬
gen (4) which gives 5 for the nitrogen. These numbers may
not, perhaps, be exactly obtained by experiment ; and they are
given merely as a general illustration of the process.
By experiments of this kind, I have determined that 100
measures of ammonia require, for saturating the hydrogen
which they contain, between 67 and 68 of pure oxygen gas,
and afford
Of hydrogen gas about 136 measures,
nitrogen gas . 47 measures.
183
The results of this analysis furnish a good example of the
condensation of the elements of gases which takes place on
chemical union ; and if we could, by any means, permanently
i.
SECT. III.
ANALYSIS OF AMMONIA.
243
condense a mixture of 136 measures of hydrogen with 47 of
nitrogen into 100 measures, the new gas would constitute am-
omonia. Simple admixture of these gases, however, even in
the same proportions which are obtained by analyzing am¬
monia, is not sufficient to generate this alkali. The caloric,
jwith which the hydrogen and nitrogen are respectively com¬
bined, opposes, by its elasticity, an obstacle to their union,
and places them beyond the sphere of their mutual attractions.
If these elements are presented to each other when one or
both are deprived of part of their caloric, combination then
takes place ; and the composition of the volatile alkali is proved
synthetically, as in the following experiment.
When iron filings, moistened with water, are exposed to
nitrogen gas confined over mercury, the gas, after some time
,has elapsed, acquires the smell of volatile alkali. In this case,
the iron decomposes the water and seizes its oxygen; while
the hydrogen, at the moment of its liberation, unites with
nitrogen and composes ammonia. This state of condensation,
or absence of the quantity of caloric necessary to bring it into
;a gaseous form, has been called the nascent state of hydrogen;
and the same term has been applied to the bases of other gases
when in a similar state.
Art. 3. — On the Presence of Oxygen in Ammonia; and on the
Amalgam of Mercury and Ammonia.
Beside the hydrogen and nitrogen which, it has already
been stated, are obtained by decomposing ammonia, it has
been conjectured by Sir H. Davy that this alkali contains,
also, a small proportion of oxygen, not exceeding seven or
eight parts in the hundred. The arguments, which he has
brought in favour of this opinion, are derived chiefly from the*
following facts :
1. When he decomposed ammonia by electricity, the gases
produced fell short, by nearly one eleventh, of the weight of
the ammonia employed; in other words 100 grains of am¬
monia gave only about 91 grains of permanent gases, io
obtain this result, however, several precautions are necessary,
r 2
244
ANALYSIS OF AMMONIA.
CHAP. vin
fe
F*
which are fully stated in the Philosophical Transactions fox
1809, p. 460.
2. By repeatedly transmitting ammoniacal gas (previous!; a
deprived, by passing it through a tube surrounded by a freez
ing mixture, of as much water as possible) over red-hot iror
w7irc, the metal became superficially oxidized, and gained i
very slight increase of weight. It is proper, however, to state. :
that a similar experiment was made by M. Berthollet, junior
with different, or at least with equivocal, results. Besides, ;
very minute addition of oxygen might be furnished to tb<
iron by the decomposition of a small portion of water, whicf
ammoniacal gas, in common with all other gases, contains?
and which would scarcely be separated from it by the tem
perature of a freezing mixture. No sufficient proof, indeed
has been established by the subsequent experiments of Sir H
Davy; by my own, directed to the same object; or by thos
of any other person, that oxygen exists as an element of am f
inonia, or that any products can be obtained by its decompo
sition, beside hydrogen and nitrogen gases.
It must be acknowledged, however, that the indirect evi
dence, in favour of the presence of oxygen as an element o
ammonia, which is furnished by other experiments of Sir H
Davy, is much stronger than that derived from the results c
its analysis. These experiments even go so far as to sugges
that ammonia may, like the fixed alkalies, be an oxide of i
peculiar metal, or at least of some compound containing th i
elements of a metal. And, as hydrogen and nitrogen alone ara
obtained by the electrical analysis of ammonia, it will follov
that the metal in question is either a compound of those tw«
bases, or a component part of one of them. If this shouk
be established, we shall obtain proof of a fact of the greates
novelty and curiosity, viz. the existence of a metal or ;
metallic oxide, whose natural state is that of an aeriform fluid.
To understand the general outline of these experiments, i
may be necessary to premise, that whenever mercury, afte t,
combination with another substance, retains in a great mea
sure its characteristic properties, and forms wdiat has beei
called an amalgam , we infer that the change has been produce
\
n
h
I;,
to
i
INSECT. IIL
ANALYSIS OF AMMONIA,
24A
by its union with a metal ; for the metals are the only bodies
r which are capable of amalgamating with quicksilver. Now it
a was found, by MM. Berzelius and Pontin of Stockholm,
s j that when mercury, negatively electrified in the Voltaic cir~
hcuit, is placed in contact with solution of ammonia, it gra¬
dually expands to four or five times its dimensions, and be¬
comes a soft solid, which, at 70° or 80° Fahrenheit, has the
[(consistence of butter. At the freezing temperature, it becomes
'[firmer, and forms a crystallized mass, in which small shining
^facets appear. By this combination, it is very remarkable
dthat mercury gains an addition of only about one twelve thou-
[isandth part of its weight ; and yet has its specific gravity so
ijmuch decreased, that from being between 13 and 14 times
c heavier than water, it becomes only three times heavier. Its
colour, lustre, opacity, and conducting powers remain unim¬
paired.
An easier mode of forming this amalgam, Sir H. Davy
(found, is to employ mercury united with a minute quantity
iof potassium, sodium, or barium. A compound of this sort,
[placed in contact with a solution of ammonia, enlarges to
i eight or ten times its bulk, and becomes a soft solid, which
Imay be preserved a much longer time than the amalgam made
^ by electrical powers, and which even changes very slowly
under water.
When this amalgam is exposed to the atmosphere, oxygen
is absorbed ; ammonia is reproduced ; and the quicksilver is
> recovered in its metallic form. When thrown into water,
ammonia is also regenerated, and quicksilver separated, hy¬
drogen gas being at the same time evolved. It appears, then,
that in the formation of the amalgam, mercury combines with
one or more of the elements of ammonia, and that in the
subsequent oxidation of what is thus acquired by the ammo¬
nia, consists the process of regenerating alkali. In this view
of the subject, there certainly appears great reason to believe
that oxygen is one of the constituents of ammonia ; but the
facts are not sufficiently simple to furnish incontrovertible evi¬
dence, and their explanation is still attended with considerable
obscurity.
On the supposition that the unknown substance, which
amalgamates with the mercury, is of a metallic nature. Sir
248 ANALYSIS OF AMMONIA. CHAP. VIII.
H. Davy proposed for it the name ammonium. All attempts
to detach it from this combination, and to exhibit it in a
separate form, have hitherto failed; and it still remains an
object of farther investigation. One great difficulty consists
in procuring the amalgam iree from water, ol which it always
contains enough to furnish oxygen, and to regenerate alkali.
The amalgam, which appears to be most free from adherings
moisture, is that of potassium, mercury, and ammonium in
a solid state; but even this amalgam gave on distillation no¬
thing but hydrogen gas, beside a small proportion of am¬
monia. The quantity of matter, added to the mercury, in
the formation of the amalgam, Sir H. Davy estimates at only
i th
1 2 0 0 0 “
Gay Lussac and Thenard * have also made a great number
of experiments on this amalgam, from which they infer that
it is a compound of mercury, hydrogen, and ammonia ; and
that mercury, to become the amalgam, absorbs 3.47 times its s
bulk of hydrogen gas, and 4.22 or 8.67 times its bulk of am-
maniacal gas. The increased levity of the mercury, they ares
of opinion, may be explained by the lightness of the elements
with which it combines, and by their being retained by so
feeble an affinity, as to produce very little condensation.
This view of the subject has been opposed by Berzelius on
theoretical grounds, for a statement of which the reader may
consult the 77th vol. of Annales de Cliimie , p. 79. In the
present state of the inquiry, new facts seem to be wanting to
determine the nature of this singular compound.
An experiment of Dobereiner would, if confirmed, prove
that hydrogen has ol itself the property of forming an amal¬
gam with mercury He introduced a globule of mercury
into a vessel of watei, and placed it near the negative wire of
a galvanic battery. Oxygen gas was given out from the posi¬
tive wire, but no gas whatever arose from the negative wire.
By this wire, the mercury was attracted and gradually con¬
verted into an amalgam fi. The experiment, however, when
carefully repeated in this country, has not been attended with
the same result
* Recherches, i. 7%.
% Phil. Mag. xlvi. 421.
4 Thomson’s Annals, vii. SO,
SECT. III.
ANALYSIS OF AMMONIA.
247
Art. 4. — Action of Potassium on Ammonia. .
When potassium is melted in ammoniacal gas, it is changed
into an olive-green fusible substance; the ammonia almost
entirely disappears ; and is replaced by a volume of hydrogen,
precisely equal to that, which the same quantity of potassium
would have disengaged from water. To effect this combina¬
tion, in the way recommended by Gay Lussac and Thenard,
a bent glass tube is employed, into which, when filled with
perfectly dry mercury, a known quantity of ammoniacal gas
is admitted, and a determinate weight of potassium is then
passed through the mercury, by means of a bent iron wire.
Care must be taken to shake off from the potassium, and
from that part of the tube which contains the gas, all the ad¬
hering globules of mercury; otherwise they interfere with
the result. The part of the tube, which contains the potas¬
sium, is next gently heated by a spirit lamp ; the metal enters
into fusion, and is covered writh a thin crust, which soon dis¬
appears : the brilliant surface of the metal then is exposed ;
it absorbs much ammoniacal gas, and, in a few instants, is
transformed into the olive-green substance. It is necessary,
at this period, to remove the lamp ; and indeed the regulation
of the heat, which can only be learned by experience, occa¬
sions considerable variety in the results, and in the quantity
of ammonia which disappears. When the gas is used in suf¬
ficient quantity, all the potassium is changed into the olive
compound; and it absorbs from 100 to 136 times its volume
of alkaline gas.
When the olive-coloured substance is gradually heated in a
glass vessel* in contact with hydrogen gas, it enters into a
kind of ebullition ; much gas is disengaged ; and the mercury
descends rapidly in the tube. When the tube is not heated
beyond a cherry red, nothing but ammonia is disengaged.
But when this degree of heat is exceeded, hydrogen and ni¬
trogen are obtained, in the proportions required to form am¬
monia, viz. 3 to 1. In all cases, the residue is blackish, and
is found to have lost its fusibility. Only three fifths, however,
of the ammonia which has disappeared, can be re-obtained by
heat, either in the form of alkaline gas or oi its elements.
ANALYSIS OF AMMONIA.
CHAP. VIII*
248
When the olive-coloured substance is brought into contact
with water in close vessels, great heat is excited, and the only
products are potash and aminoniaeal gas, the latter in exactly
the same quantity which was originally absorbed, except a
few hundredth parts, which are absorbed by the moist potash.
The only caution, necessary to obtain this result, is not to
use more water than is absolutely necessary.
Precisely similar phenomena occur, when sodium is heated
in ammoniacal gas ; the sodium is transformed into an olive-
green substance; ammonia is absorbed, and hydrogen is
evolved, in exactly the same quantity as by the action of an
equal weight of sodium on water.
The experiments of Sir H. Davy on the olive-coloured
compound agree, in the main, with those of Gay Lussac and
Thenard. By distillation per se, he obtained some unde¬
composed ammonia, and hydrogen and nitrogen gases in the
proportion by volume of 2-t- of the former to I of the latter.
He examined the residue of its distillation with much atten¬
tion ; and describes it to be a black, shining, opaque, and
brittle substance, highly inflammable when exposed to air at
the ordinary temperature. When submitted by itself to dis¬
tillation at a strong heat, in a platinum tube (which was done
with the expectation that nitrogen gas only would have been
evolved), a mixture of gases was obtained, consisting of only
one fifth nitrogen, and four fifths hydrogen, without any
ammonia ; and potash remained in the tube.
Though these facts cannot be easily explained, except on
the supposition that nitrogen is an oxide ; yet (as is candidly
acknowledged by Sir H. Davy), in processes so delicate and
complicated, and involving such numerous data, wre cannot
be certain that every source of fallacy has been avoided, and
every circumstance observed and reasoned upon.
CHAPTER IX.
EARTHS.
The term earth was, till lately, employed ‘ to denote a
tasteless, inodorous, dry, brittle, and uninflammable sub¬
stance, not more than five times heavier than water.” This
definition, however, was rendered imperfect by the discovery,
that certain earths have a strong taste, and are readily soluble
in water, which yet possess the other characters of earthy
bodies. Some of the earths were therefore removed from this
class, and arranged among the alkalies. The classification,
however, which appears to me most eligible, is that which
divides them into earths simply, and alkaline earths; the latter
partaking of the characters both of earths and alkalies. The
alkaline earths are Barytes, Strontites, Lime, and Magnesia.
The earths are Silex, Altimine, Zircon, Glucine, andYttria*.
Until the important sera of Sir EL Davy’s discoveries, the
earths were, with respect to the state of our knowledge, simple
or elementary bodies. Many conjectures, it is true, had been
formed respecting their nature ; and, among these we find
that their being composed of oxygen and a metallic base had
been suggested as a probable theory f. Led by the analogy
arising from his experiments on the alkalies, Sir El. Davy,
however, was the first to demonstrate what had before been
only imagined; and to disunite, by the agency of strong
eletrical powers, tiie constituent principles of several of this
class of bodies.
In this part of lire investigation, difficulties were encoun¬
tered which demanded great perseverance and complicated
processes. The affinity of the earthy bases for oxygen ap¬
pears considerably to surpass that of the metals composing
potash and soda; and it was found that simple exposure to
* The Agustine of Tromsdorff has been shown, by Berthohet, to be
merely Phosphate of Lime. Nicholson’s Journal, 8vo. vii. 117.
f The reader may consult a history of opinions respecting the earths, in
a note to Sir H. Davy’s paper, Philosophical Transactions, 1808.
ANALYSIS OF THE EARTHS.
CHAP. IX.
the opposite electricities was not adequate to the separation of
the principles which compose the earths; or, at least, that
the effect was too indistinct to furnish satisfactory evidence of
their nature. Sir H. Davy was, therefore, induced to electrify
the earths, as he had formerly operated on potash, in contact
with the oxides of known metals; with the expectation that
the metallic base of the earth would unite with the metal con¬
tained in the oxide he employed, and form an alloy. Thus a
mixture of barytes and red oxide of mercury might be ex¬
pected to yield an alloy of mercury with the metallic base of
barytes; and such, in fact, was the result of the experiment;
for a solid amalgam adhered to the negative wire, which,
when thrown into water, evolved hydrogen, leaving pure
mercury, and a solution of barytes. Mixtures of lime, stron-
tites, or magnesia with oxide of mercury gave similar amal¬
gams, from which the respective alkalies were regenerated by
the action of air or water; but the quantity obtained was too
minute for investigation.
On the suggestion of Professor Berzelius of Stockholm,
the earths were next electrified negatively in contact with
mercury itself; and in this way amalgams _ were obtained from
barytes, strontites, lime, and magnesia. These compounds
of mercury with the metallic base of the earths decomposed
water, and the earth, which had afforded them, was rege¬
nerated. Under naphtha, they might be preserved for a con¬
siderable time ; but at length they became covered with a
white crust of the regenerated earth.
To procure quantities of these amalgams sufficient for dis¬
tillation, the earths were slightly moistened, and mixed with
one third of red oxide of mercury : the mixture was then
placed on a plate of platinum, a cavity was made in the upper
part of it to receive a globule of mercury of from 50 to 60
grains in weight, and the whole was covered with a thin film
of mercury ; lastly, the plate was made positive, and the
mercury negative, by a proper communication with a battery
of 500 pairs.
From these amalgams, the mercury was separated by dis¬
tilling in small tubes of glass filled with the vapour of naphtha.
Considerable difficulties, however, attended these operations;
CHAP. IX.
ANALYSIS OP THE EARTHS.
251
and after all, Sir H. Davy could, in no case, be absolutely
certain, that there was not a small quantity of mercury in
combination with the metals of the earths.
The proportion of oxygen and metal has not yet been as¬
certained in any of the earths ; but the evidence from analysis
of their composition is perfectly satisfactory, the inflammable
base appearing uniformly at the negative surface in the Voltaic
circuit, and the oxygen at the positive surface.
The decomposition of the other earths, al amine, si lex,
zircon, and glucirie was not effected by the same means, that
had been applied successfully to the alkaline earths. Combi¬
nations of potash and alumine, and of potash and silex, were
electrified with the hope that the bases of these earths would
be obtained in the state of an alloy with potassium. Soda
and zircon were similarly treated. In all these cases, the
phenomena indicated that some portion of the several earths
had been decomposed ; hut in too minute a quantity to exa¬
mine the properties of their bases.
.Lastly, potassium, amalgamated with about one third its
weight of mercury, was electrified negatively under naphtha,
in contact with the four earths, which were last enumerated.
The potassium generated was thrown into water, and the
alkali produced saturated with acetic acid. Now if any metal
had thus been obtained from the earths, it would exist in the
form of an alloy with potassium ; both metals would be oxy-
dized by the water ; the potassium would reproduce potash,
and the other metal the earth which gave it origin, which
earth would be dissolved by the solution of potash, and would
reappear on adding an acid. The general tenor of the results
gave great reason to conclude that alumine, silex, glucine,
and zircon are, like the alkaline earths, metallic oxides.
By the use of the blow-pipe with compressed oxygen and
hydrogen gases, Professor Clarke of Cambridge was led to
believe that he had succeeded in effecting the decomposition of
the earths, and in exhibiting their metallic bases in a separate
form *. The experiments, however, have been frequently re-
* Thomson’s Annals, viii. 313, 357, 471 ; ix. 194. Journal of Science,
&c. ii. 119.
2
252
EARTHS.
CHAP. IX.
peatcd in the laboratory of the Royal Institution, but always
without success, though the heat obtained was sufficient for
the fusion or corundum, rock crystal, and other refractory
bodies *. It is probable, therefore, that Dr. Clarke may have
been misled by the presence of some impurities in the earths,
which were submitted to his experiments. But in a subsequent
memoir f, he declares his conviction of the accuracy of his
results to be strengthened by carefully repeated experiments,
hi which a distinct metallic film was produced on the surface
of barytes, and was found to give no traces of iron or zinc
deposited (as had been suggested) by the hydrogen gas.
SECTION I.
Barytes.
Barytes may be obtained in a state of purity, by the calcina¬
tion of its carbonate or nitrate, in a manner which will be
hereafter described. (See chap. xi. sect. 4, art. iv.) It exhibits,
when pure, the following properties.
I. Barytes, in a pure form, has a sharp caustic taste; changes
vegetable blue colours to green ; and serves as the intermedium
between oil and water. In these respects, it bears a strong
resemblance to alkalies.
II. When exposed to the flame of the blow-pipe on char¬
coal, it melts ; boils violently ; and forms small globules, which
sink into the charcoal. After being kept in fusion in a cru¬
cible during ten minutes, it still, according to Berth ollet, con¬
tains 9 per cent, of water; from theory it should contain 10.59
per cent. This, however, is true only of barytes which has
been obtained from the carbonate, by a process to be described
hereafter. Barytes, procured by decomposing the nitrate of
that earth, is not fusible, and appears to contain little if any
water
III. If a small quantity of water be added to recently pre¬
pared barytes, it is absorbed with great rapidity ; prodigious
* Journal of Science, ii. 461.
J Nicholson’s Journal, xxiii. 281,
f Thomson’s Annals, x. 133, 375.
SECT. I.
BARYTES.
253
heat is excited; and the water is completely solidified, a sort
of hard cement being obtained. A little more water converts
this mass into a light bulky powder; and, when completely
covered with water, the barytes is dissolved. Boiling water
should be employed for this purpose; unless sufficient tem¬
perature has been produced, by the sudden addition of the
whole quantity necessary for solution.
IV. When the solution, prepared with boiling water, is
allowed to cool slowly, it shoots into regular crystals. These
have the form of flattened hexagonal prisms, having two broad
sides, with two intervening narrow ones; and terminated, at
each end, by a quadrangular pyramid. They lose, according
to Bucholz, half their weight of water in a red heat; the
barytes then continues fused, and parts with no more water,
though still combined with the proportion above stated. Mr.
Dalton, from his experiments, infers that the crystals contain
SO barytes and 70 water per cent., which would make them
consist of 1 atom of barytes 4- 20 atoms of water.
V. The crystals are so soluble, as to be taken up, when
heated, merely by their own water of crystallization. When
exposed to a stronger heat, they swell, foam, and leave a dry
white powder, amounting to about 47 parts from 100 of the
crystals. This again combines with water with great heat and
violence. At 60° of Fahrenheit, an ounce measure of water
dissolves only 25 grains of the crystals, i. e. they require for
solution, 174- times their weight of water. Exposed to the
atmosphere, they effloresce, and become pulverulent.
VI. When added to spirit of wine, and heated in a spoon
over a lamp, they communicate a yellowish colour to its flame.
VII. The specific gravity of this earth, according to Four-
croy, is 4 ; but Hassenfratz states it at only 2.374. The former
account, however, is the more probable. All its combina¬
tions have considerable specific gravity; and hence its name
is derived, viz . from the Greek word fiapug signifying heavy.
The weight of its atom Mr. Dalton states at 68, but this num¬
ber is probably rather too low, as will appear in the sequel.
VIII. Barytes does not unite with any of the alkalies.
Of the lase of barytes , or barium,-— The base of barytes was
3
254?
Earths.
CHAP. IX.
obtained by Mr. Davy by distilling its amalgam, obtained in
the following manner. A quantity of native carbonate of
barytes was made into a paste with water, and placed on a
tray of platinum ; a cavity was made in the paste to receive a
globule of mercury, which was rendered negative, at the same
time that the platinum was made positive by means of a Voltaic
battery, containing about 100 double plates. In a short time,
an amalgam was formed consisting of mercury and barium.
This amalgam was introduced into a little tube made of glass
free from lead, which wras bent into the shape of a retort, then
filled with the vapour of naphtha, and hermetically sealed.
Heat was then applied to the tube, till ail the mercury was
driven off.
The residuum of this distillation was a dark grey metal, with
a lustre inferior to that of cast iron. At the ordinary tem¬
perature of the air it remained a solid ; but became fluid at
a heat below redness. It did not rise in vapour, till heated
nearly to redness, and then acted violently upon the glass.
When exposed to the air, this substance rapidly tarnished,
and fell into a white powder, which was barytes. When this
process was conducted in a small portion of air, the oxygen
was absorbed; and the nitrogen remained unaltered. A por¬
tion of it thrown into water acted upon it with great violence,
and sank to the bottom, producing barytes, and evolving
hydrogen gas.
The quantities obtained were too minute for an examination
either of its physical or chemical qualities. It sank rapidly
in water, and even in sulphuric acid, though surrounded by
globules of hydrogen equal to two or three times its volume.
Hence it is probable that it cannot be less than four or five
times as heavy as water. It was flattened by pressure, but
required considerable force for this effect.
The proportion of the components of barytes Sir H. Davy
deduces to be 89.7 barium and 10.3 oxygen per cent. The
determination of Berzelius nearly agrees with this, viz.
Barium .... 89.52 .... 100.00
Oxygen. . . . 10.48 .... 11.69
100.
111.69
I SECT. II.
STRONTITES.
255
j
r
j
(
i
r
i
!
■
Barium, from the experiments of Gay Lussac and Thenard,
appears capable of combining with a larger quantity of oxygen
than exists in barytes ; for when pure barytes, prepared from
the nitrate, was heated in dry oxygen gas, the gas was rapidly
absorbed, and the earth became grey, and appeared glazed
on its suface.
On the supposition that barytes consists of an atom of
barium united with an atom of oxygen, the atom of barium,
should weigh 64, and that of barytes 71.5. The second oxide
probably contains an additional atom of oxygen ; and its atom,
in that case, will weigh 79.
SECTION II.
Strontites .
I. Strontites (called also Strontia, from Strontian in
Scotland, the place where it was first discovered, in combina¬
tion with carbonic acid) resembles barytes in many of its pro¬
perties ; and all that is included in the first three paragraphs
of the last section may be applied, also, to this earth.
II. Like barytes, strontites is readily soluble in boiling
water ; and the solution, on cooling, affords regular crystals ;
but the shape of these differs considerably from that of barytic
crystals. The crystals of strontites are thin quadrangular
plates ; sometimes square, oftener parallelograms : not exceed¬
ing in length, and not reaching in breadth, a quarter of an
inch. Sometimes their edges are plain, but they oftener consist
of two facets, meeting together, and forming an angle like the
roof of a house. They adhere to each other in such a manner
as to form a thin plate, of an inch or more in length, and half
an inch in breadth. Sometimes they assume a cubic form.
III. These crystals undergo, by the action of heat, much
the same changes as those of barytes ; and leave only about
32 per cent, of the dry earth. One part of the crystals re¬
quires about 514- of water at the temperature of 60° for solu¬
tion, but boiling water takes up half its weight. Mr. Dalton
supposes the crystals to consist of I atom of strontites and 12
atoms of water.
256
EARTHS.
CHAP. JX.,
IV. Boiling alcohol, with the addition of these crystals, ,
burns with a blood red flame.
V. Strontites does not combine with alkalies. Barytes has ;
no affinity for it; for no precipitation ensues, on mixing the
watery solutions of the two earths.
From the preceding enumeration of its characters, it ap¬
pears that strontites differs from barytes in the form of its
crystals, which contain also more combined water, and are
less soluble than those of barytes ; and also in affording, with
alcohol, a flame of different colour. These distinctions were
deduced by Dr. Hope, from his excellent series of experi¬
ments on the two earths *. Other circumstances of distinction,
derived from the properties of their respective salts, will be
stated hereafter.
Of the base of strontites or strontium. — Strontium may be
procured by exactly the same process as barium, substituting
the native carbonate of strontites for that of barytes. It was
first obtained by Sir H. Davy in 1808, but in very minute
quantities. It resembled barium, had not a very high lustre,
was diflicultly fusible, and not volatile. It was converted into
strontites by exposure to air, or by contact with wviter.
The product of its oxidation, strontites, Sir FI. Davy thinks
it probable is composed of 86 strontium and 14 oxygen. In
this case, 45 wrould be nearly the weight of the atom of stron¬
tium, and 52.5 that of the atom of strontites. Stromever has
•/
lately deduced its composition to be
Strontium . . 84.669 or 100.000
Oxygen.... . 15.331 18.107
100.
And, taking with Dr. Wollaston, 10 as the equivalent of oxy¬
gen, he makes the number for strontium to be 55.2, and for
strontites 65.2 f.
* See Edinburgh Transactions, vol. iv. f Ann. de Ch. et Ph. iii. 397.
/
SECT. Ill,
LIME,
257
SECTION III.
Lime .
I. Its external qualities. — -These may be exhibited in com*
Imon quicklime, such as is employed for the purposes of build¬
ing or agriculture. In the same state, it is sufficiently pure
for demonstrating its chemical properties ; but, when used for
purposes of the latter kind, it should be fresh burnt from the
kiln. For accurate experiments, it should be prepared by
calcining Carara or Parian marble in a crucible for several
hours. Its specific gravity is 2.3. It requires an intense heat
for its fusion, and is not volatile.
II. Relation of lime to water .
[a) Lime absorbs water very rapidly with considerable heat
ii and noise. This may be shown by sprinkling a little water on
some dry quicklime. The above-mentioned phenomena will
s; take place, and the lime will fall into powder, which has been
; called hydrat of lime . In this compound, the lime is to the
water, according to Mr. Dalton, as 23 to 8; according to
1 Davy, as 55 to 17; and to Berzelius, as 100 to 32.1. Some
care, however, is necessary in its preparation, lest more water
[j should be added, than is essential to its constitution. It
affords a very convenient form of keeping lime, for occasional
use in a laboratory ; for the hydrat may safely be preserved in
glass bottles, which are almost constantly broken by the earth
in its perfectly dry state. The hydrat of lime differs from those
of barytes and strontites, in retaining its water much less
forcibly; for the whole of it may be expelled by a strong red
heat.
The degree of heat, produced by the combination of lime
with water, is supposed by Mr. Dalton to be not less than
800°, and is sufficient to set fire to some inflammable bodies ;
and when a large quantity of lime is suddenly slaked in a
dark place, even light, according to Pelletier, is sometimes
evolved. The caloric, which is thus set at liberty, is doubt¬
less that contained in the water, and essential to its fluidity.
By combination with lime, water passes to a solid state, and
probably even to a state of much greater solidity than that of
VOL. I. s
$
258
EARTHS.
CHAP. IX.
ice. Hence, during this change, it evolves more caloric than
dnrin g conversion into ice; and hence even ice itself, when
mixed with quicklime, in the proportion of one to two, enters
into a combination which has its temperature raised to 212°.
When a sufficient quantity of water has been added to reduce
lime into a thin liquid, this is called milk or cream of lime .
Lime is, in some degree, convertible into vapour by com¬
bination with water. When a piece of moistened paper,
stained with the juice of the violet, is held in the steam,
which arises from lime suddenly slaked, its colour is changed
from blue to green, Hence the smell wffiich is perceived
during the slaking of lime.
(b) Lime absorbs moisture from the atmosphere, and falls
gradually into powder, containing pure lime and water, in
the proportion nearly of 100 to 32.
(c) Lime is very sparingly soluble in water, viz. in the pro¬
portion of about 1 to 500 ; according to Thomson, 1 to 758 ;
to Davy, 1 to 450 ; and to Dalton, at 60° Fahrenheit, 1 to
778. The experiments of Mr. Dalton tend to establish a
curious fact respecting the solubility of lime, viz. that it
dissolves more plentifully in cold than in hot water. He has
given the following table, the first column of which expresses
the temperature of the water; the second, the number of
grains of water, required to take up one grain of lime ; and
the third, the number required to dissolve one grain of hydrate
of lime.
Grains of water Grains of water
Temperature. that dissolve that dissolve
1 gr. of lime. 1 gr. of hydrate.
60° . . . . 778 . .\ 584
130° . 972 . 720
212° . . . 1270 . 952
At the freezing point, or nearly so, Mr. Dalton thinks it
probable that water would take up nearly twice as much
lime, as is dissolved by boiling water.
Lime, when thus dissolved, forms what has been termed
lime-water. This solution tastes strongly of lime, turns vege¬
table blues to green, and unites with oil, forming an imper¬
fect soap. To prepare the solution, lime is to be slaked to a
thin paste, and a sufficient quantity of water afterwards added.
The mixture is to be stirred repeatedly, the lime allowed to
SECT. III.
LIME
259
settle, and the clear liquor decanted for use. It must be pre¬
served in closely stopped vessels, for reasons which will be
stated in the chapter on carbonic acid.
(d) When lime water is freely exposed to the atmosphere,
the lime is precipitated from it in the state of a carbonate ;
: and it is, therefore, not possible to obtain crystals of pure
lime, by evaporating lime water in the common way. Its
crystallization, however, has been effected by Gay Lussac,
i by inclosing a vessel of lime water, and another of concen-
i trated sulphuric acid, under the same glass receiver *. The
i evaporation of the water goes on quickly, especially when the
i sulphuric acid is occasionally renewed, and small transparent
i crystals are obtained in regular hexahedrons, cut perpendi-
i cularly to their axes. They remain transparent when exposed
! to the air for a few days, and are then changed into carbonate
i of lime. By ignition in a glass tube, their water of crystal-
1 lization is expelled, and they are proved to consist of
Lime . 76.26 . 100
Water . .23.74 . 31.14
100.
These crystals agree, therefore, very nearly in composition
J with the hydrate (or hydroxure , as Gay Lussac proposes to
i call it) which is obtained by exposing quicklime to a damp
j atmosphere. This, if the atom of water be taken at 8.5,
i would make the atom of lime 26.5, and that of the hydrate
! 35. Or, taking oxygen with Dr. Wollaston as 10, and the
i equivalent of water to be 11.32, the equivalent of lime will
I be 35.46, and that of the hydrate 46.78.
Lime does not combine, in any notable proportion, with
I the alkalies or earths already described, except by fusion.
The base of lime , to which Sir H. Davy has given the name
of calcium , he has never been able to examine, exposed to air
or under naphtha. In the case, in which he was able to distil
the quicksilver from its amalgam, to the greatest extent, the
tube unfortunately broke whilst warm ; and, at the moment
that the air entered, the metal, which had the colour and
* Ann. de Chim, et Phys, i. 3^4.
s 2
26©
EARTHS.
CHAP. IX.
lustre of silver, instantly took fire, and burnt, with an in¬
tense white light, into lime.
There appears to be only one compound of calcium and
oxygen, viz . lime ; and, in this, the oxygen is to the metal,
according to Sir H. Davy, as 7.5 to 20. Berzelius electrified
lime liquor in contact with mercury, and obtained an amal¬
gam of mercury with calcium. On this, water was made to
act ; and, from the quantity of lime that was formed, he esti¬
mated its composition to be,
Calcium ..... .71.73 ....... .100
Oxygen . 28.27 . 39.4
100 139.4
This would make the atom of calcium to weigh 20, and the
atom of lime 27.5, and of the hydrate 36.
SECTION IV.
Magnesia .
Magnesia possesses the properties of an alkali, but in a
considerably less degree than any of the foregoing earths. Its
characters are as follow :
I. When perfectly pure, it is entirely destitute of taste and
smell. Its specific gravity is between 2 and 3.
II. No heat is excited by the affusion of water, and only a
very small proportion, not exceeding a 2000th its weight, of
the earth is dissolved. Magnesia appears, however, to have
some affinity for water ; for when moistened, and afterwards
dried, its weight is found increased in the proportion of 1 1 8
to 100. When precipitated by pure potash or soda from any
of its salts, it falls down in union with water as a hydratey
which, when dried by a very gentle heat, forms transparent
masses. In this state, according to Davy, it contains about
£ of its weight of water; or, according to Berzelius, 100
parts of magnesia absorb from 142 to 144 of water.
III. Magnesia changes to green the blue colour of the
violet; but the watery solution of magnesia, when filtered
SECT. V.
MAGNESIA.
261
through paper, does not produce a similar effect. In this
respect it differs from lime. It reddens turmeric like the
alkalies.
IV. It is not dissolved by liquid alkalies, nor by alkaline
earths; and in the dry way, it has no affinity for barytes or
strontites.
The base of magnesia , for which Sir H. Davy has proposed
the term magnesium , is but imperfectly known. In the
attempts to distil its amalgams, the metal seemed to act upon
the glass, even before the whole of the quicksilver was dis¬
tilled from it. In one experiment, in which the process was
stopped, before the mercury was entirely driven off, it ap¬
peared as a solid, having the same whiteness and lustre as the
other metals of the earths. It sunk rapidly in water, though
surrounded by globules of gas, and produced magnesia. In
the air, it quickly changed, becoming covered with a white
crust, and falling into a white powder, which proved to be
magnesia. This earth Berzelius states, in round numbers, to
consist of 38 or 39 per cent, oxygen, and 61 or 62 magnesium*
SECTION V.
Silex,
I. Siliceous earth, or silex, may be obtained tolerably pure
from flints by the following process:— Procure some common
gun-flints, and calcine them in a crucible in a low red heat.
By this treatment they will become brittle, and easily redu¬
cible to powder. Mix them, when pulverized, with three or
four times their weight of carbonate of potash, and let the
mixture be fused in a strong red heat, in a crucible. The
materials must bear only a small proportion to the capacity
of the crucible; and the heat must at first be very moderate,
and slowly increased. Even with this precaution, the mass,
on entering into fusion, will be apt to overflow ; and must be
pressed down as it rises, by an iron rod. When this effer¬
vescence has ceased, let the heat be considerably raised, so
262
EARTHS.
CHAP. IX.
that the materials may be in perfect fusion during half an
hour, and pour the melted mass on a copper or iron dish.
We shall thus obtain a compound of alkali and siliceous earth.
Dissolve this in water, filter the solution, and pour it into
diluted sulphuric or muriatic acid. An immediate precipita¬
tion will ensue, and, as long as this continues, add fresh por¬
tions of the solution. In precipitating the alkaline solution
of silex, more acid must be used than is sufficient to engage
the alkali ; and the alkaline liquor must be added to the acid,
and not the reverse; for, in the latter case, the precipitate
will be glass, and not silex. Let the precipitate subside, pour
off the liquor that floats above it, and wash the sediment with
hot water, till it comes off tasteless. Then dry it.
Silex, obtained by this process, though pure enough for
the following experiments, may still contain a portion of
alumine. To separate the latter earth, boil the precipitate
with diluted sulphuric acid, to which a little sulphate of pot¬
ash may be added. The alumine will thus be dissolved ; and
the silex may be freed from the solution of alum by repeated
washings with water. Even silex, however, that has been
most carefully washed, still gives traces of potash on the
application of electro- chemical powers. (Davy.)
II. Siliceous earth, as thus obtained, has the following qua¬
lities :
(a) It is perfectly white and tasteless. It is infusible by the
intense heat of Voltaic electricity * ; but was melted by Dr.
Clarke with the oxygen and hydrogen blow-pipe. To a
certain degree it appears to be volatile, for a filamentous sub¬
stance, collected from iron furnaces, and resembling amianthus,
was found by Vauquelin to be pure silex.
(/;) When mixed with water, it does not form a cohesive
mass like alumine, and has a dry and harsh feel to the fingers.
It retains, when fresh precipitated, about 26 per cent, of
water, after being dried at 70° Fahrenheit. But, according
to Berzelius, this water is not chemically combined.
(c) It is insoluble in water. Yet, when fresh precipitated,
water has the property of retaining in solution about one
* Phil. Trans. 1815, p. 370.
13ECT V. silex„ 2 63
thousandth of its weight That silex, however, is dissolved
in water by processes of nature, can scarcely be doubted,
when it is considered, that it is found, in considerable quan¬
tities, in a crystallized form.
(d) It is not acted on by any acid, except the fluoric. Sul¬
phuric acid poured on this compound, according to Dalton,
expels the fluoric acid, but does not unite with the silex. But
though the earth itself is not dissolved by acids, yet when
first combined with an alkali, it unites with several acids,
forming triple salts f. When fresh precipitated, however.
Dr. Marcet asserts, that it is sparingly soluble in most acids ;
and, for this reason, he recommends, in analysis, to precipi¬
tate silex by muriate of ammonia, which does not, like the
acids, redissolve it.
(e) When prepared in the foregoing manner, and very
minutely divided, silex is taken up by a solution of pure pot¬
ash, or of soda, but not by ammonia. In the aggregated
state of flints, howrever, it is perfectly insoluble in this way by
alkaline solutions ; an excellent illustration of the principle
that a very minute division of solid bodies, by presenting a
greater surface to the action of fluids, facilitates solution.
( f ) When mixed with an equal weight of carbonate of
potash, and exposed to a strong heat in a furnace, it forms a
glass, insoluble in water, and identical in all its properties
with the glass commonly manufactured. It is owing to the
siliceous earth which it contains, that glass is decomposed by
the fluoric acid. Glass, however, has occasionally other in¬
gredients, besides the two that have been mentioned J.
(g) With a larger proportion of alkali, as three or four
parts to one of silex, this earth affords a compound called,
by Dr. Black, silicated alkali . This compound, formed by
the process which has been just described, is soluble in water,
and affords a good example of the total change of the pro¬
perties of bodies by chemical union ; for, in a separate state
no substance whatever is more difficult of solution than silex.
The solution of silicated alkali was formerly termed, liquor
* See Klaproth’s Contributions, i. 399, 400. f 81 Ann. de Chira. 239.
X See Guyton, Ann. de China, vol. Ixxiii.
f64
EARTHS.
CHAP. IX.
silicum , or liquor of flints . Acids seize the alkali, and pre¬
cipitate the silex, which is even separated by mere exposure
to the atmosphere, in consequence of the absorption of car¬
bonic acid by the alkali. Without attention to the circum¬
stances mentioned in speaking of its preparation, glass, and
not silex, is separated by acids
( h ) Barytes, or strontites, and silex combine together, in
a manner similar to the union of this earth with alkalies ; but
the combination has not been applied to any useful purpose.
(i) When a solution of silex in potash is mingled with one
of barytes, of strontites, or of lime in water, or of alumine
in alkali, a precipitation ensues. Hence silex may be inferred
to have an affinity for all these earths, in the humid way.
The composition of these precipitates is stated by Mr. Dalton
in his System, p. 541.
In consequence of its possessing a stronger affinity for
alkalies and earths than for acids, as well as from its other
habitudes, silex has been thought to present a closer analogy
with acids than with earths, and in a chemical arrangement
to be more properly placed in the former class, than in the
latter. On the other hand, as it is deficient in some of the
characters which have hitherto been deemed essential to aci¬
dity, I have not thought it expedient to remove it from the
place which it has hitherto held in chemical arrangements.
Base of Silex . — In his attempts to obtain the base of silex,
or silicium , in a state of separation, Sir H. Davy has hitherto
been unsuccessful ; though the results of his experiments leave
little room to doubt that this earth is, like the rest, a metallic
oxide.
Berzelius decomposed silex, by fusing it with charcoal and
iron in a blast furnace. He obtained an alloy of iron and
silicium , which, by the action of a diluted acid, gave more
hydrogen than the same weight of iron f. This process was
successfully repeated by Stromheyer, and the properties of the
* See Dalton, p. 538.
f 81 Ann. Gh. 179. See also his account of an attempt to analyze
silica, in 40 Phil. Mag. 201.
SECT. VI.
ALUMINE.
265
different alloys investigated. He recommends the fusion of
7 parts of iron, 5 of silex, and from £ to T8(Tths of a part of
soot. From the results of acting on the alloy by dilute acids,
Berzelius infers silex to consist of
Silicium . . 45.92 . . .100
Oxygen . . .54.08 . 1 17.38
100. 217.38
And Sir H. Davy deduces the proportions to be 31 of
metal to 30 oxygen. These numbers, however, can be con¬
sidered in no other light than as approximations ; but since,
according to recent experiments*, three parts of potassium
are required to decompose one of silex, that earth cannot con¬
tain much less than half its weight of oxygen. The base,
Sir H. Daw now believes not to be a metal, but a substance
most resembling boron ; and like it, bearing an analogy to
charcoal, sulphur, and phosphorus.
SECTION VL
Alumine.
I. Alumine may be obtained free from other earths, but still
combined with carbonic acid, by precipitating a solution of
alum in water by the bi-carbonate of potash. To secure its
complete purification from sulphuric acid, Guyton advises
that the precipitate be re-dissolved in nitric acid, that nitrate
of barytes be cautiously added to the solution, till it no longer
occasions milkiness, and that the alumine be afterwards pre¬
cipitated, or separated from the nitric acid by heat f. Elec¬
tro-chemical analysis, however, in this as in many other in¬
stances, shows the imperfection of the common methods of
separating bodies from each other; for the most carefully
prepared alumine yields the metals of soda and potash, when
negatively electrified in contact with mercury J. Berzelius,
* Phil. Trans. 1814, p. 67. f Ann. de Chim. xxxii. 64.
f Davy, Philosophical Transactions, 1808.
266
EARTHS.
CHAP. IX.
also, found that when alumine is precipitated either from the
sulphate or nitrate, it is contaminated with those acids ; but
not with the muriatic, when thrown down from the muriate
of alumine by ammonia. Gay Lussac recommends the pre¬
paration of alumine by exposing that kind of alum which has
ammonia for its base, first to a gentle heat to expel the water
of crystallization, and afterwards to a red heat, which leaves
the alumine pure
II. Alumine has the following properties :
1 . It is destitute of taste and smell.
2. When moistened with water, it forms a cohesive and
ductile mass, susceptible of being kneaded into a regular form.
It is not soluble in water ; but retains a considerable quantity,
and is, indeed, a hydrate, containing, when dried at the tem¬
perature of the atmosphere, almost half its weight of water.
Even after ignition, alumine has such an affinity for moisture,
that it can hardly be placed on the scale, without acquiring
weight. Berzelius found that 100 parts of alumine, after
being ignited, gained 15-J- from a dry atmosphere, and S3 from
a humid one. For full saturation, 100 grains of alumine, he
ascertained, require 54- of water f.
3. It does not affect blue vegetable colours.
4. It is dissolved by the liquid fixed alkalies, and is precipi¬
tated by acids unchanged. In ammonia, it is very sparingly
soluble. It is not soluble in alkaline carbonates.
5. Barytes and strontites combine with alumine, both by
fusion and in the humid wav. In the first case, the result is
a Greenish or bluish coloured mass. In the second two com-
O
pounds are formed. The first, containing an excess of alu¬
mine, is in the state of an insoluble powder; the other, having
an excess of the alkaline earth, remains in solution. Alumine
may be united, by fusion, with the fixed alkalies, and with
most of the earths.
6. Alumine, as will be afterwards shown, has a strong affi¬
nity for colouring matter.
7. Alumine has the property of shrinking considerably in
bulk, when exposed to heat, and its contraction is in propor-
* Ann. deChim. et Phys. v. 101.
t 82 Ann. de Chira. 14.
SECT. VI.
ALUMINE.
267
tion to the intensity of the heat applied. On this property is
founded the pyrometer of Wedgwood , which measures high
degrees of heat, by the amount of the contraction of regu¬
larly shaped pieces of china clay. The pieces of clay are
small cylinders, half an inch in diameter, flattened on the
under surface, and baked in a low red heat. The contraction
of these pieces is measured, by putting them between two
fixed rulers of brass or porcelain, twenty-four inches long,
half an inch distant from each other at one end, and three
tenths of an inch at the other. The rulers are divided into
240 equal parts, called degrees, which commence at the wider
end; and each of which is equal to 130° of Fahrenheit. When
the clay piece is fixed in its place, before exposure to heat, it
is stationary at the first degree, which indicates about 1077°
of Fahrenheit. After being strongly heated, in a small case
which defends it from the fuel, its bulk is diminished, and it
slides down, between the converging rulers, till stopped by
their approach. The number on the graduated scale, oppo¬
site to the upper end of the piece, indicates the degree of heat
to which it has been exposed. In the appendix, rules may be
found for reducing the degrees of Wedgwood’s pyrometer to
those of Fahrenheit’s thermometer. It is proper, however,
to remark that this instrument is a much less accurate mea¬
surer of heat than was long supposed ; and that its contraction
is influenced not merely by the degree of heat to which it is
exposed, but by the mode of its application.
Almost every thing that has been said respecting the base
of silex is true, also, of that of alumine; for Sir H. Davy
attempted the decomposition of the two earths by much the
same processes. All that his results afford, is a strong pre¬
sumption that alumine is a metallic oxide; but its base, cdu-
mium , lias not been yet obtained in such a state as to make it
a fit object of investigation. Yet alloys have been formed,
which give sufficient evidence of its existence; and the pre¬
sence of oxygen in alumine is proved, by its changing potas¬
sium into potash, when ignited with that metal.
268
EARTHS.
CHAP. IX.
SECTION VIL
Zircon,
1. This earth was discovered by Klaproth in the year 1789,
in a precious stone from the island of Ceylon, called Jargon
or Zircon ; and has since been detected in the hyacinth. It
may be obtained by the following process :
Reduce the hyacinth to fine powder, which may be done in
an agate mortar, after previously igniting the stone, and
plunging it into cold water, to render it brittle. Mix the
powder with nine times its weight of pure potash ; and pro¬
ject it, by a spoonful at once, into a red-hot crucible, taking
care not to add fresh portions till the former ones are melted.
When the whole is in fusion, increase the heat for an hour,
or an hour and a half. When the crucible has cooled, break
it, and detach its contents ; reduce them to powder, and boil
them with distilled water. Let the insoluble part subside ;
decant the clear liquor, and wash the sediment with water,
till the washings cease to precipitate muriated barytes. On
the residuum pour muriatic acid to excess, and boil it during
a quarter of an hour; filter the liquor, and evaporate to dry¬
ness in a leaden vessel. Re-dissolve the dry mass; filter again,
and precipitate the zircon with carbonate of soda. The car¬
bonate of zircon is thus obtained, from which the carbonic
acid may be expelled by calcination.
II. Zircon has the following properties :
] . It has the form of a fine white powder, which has some¬
what of the harsh feel of silex, when rubbed between the
fingers. It is entirely destitute of taste and smell. Its specific
gravity exceeds 4.
2. It is insoluble in water ; yet it appears to have some affi¬
nity for that fluid, for it retains, when slowly dried after pre¬
cipitation, one third its weight, and assumes a yellow colour
and slight transparenc}', like that of gum arabic.
3. It is insoluble in pure liquid alkalies ; nor does it even
combine with them by fusion ; but it is soluble in alkaline car¬
bonates. In the foregoing process, therefore, the carbonate
of soda should not be added to excess.
3
SECT. VIII.
GLUCINE.
269
4. Exposed to a strong heat, zircon fuses, assumes a light
grey colour ; and such hardness, on cooling, as to strike fire
with steel, and to scratch glass, or even rock crystal.
5. Its action on other earths has not been fully investigated.
6. It is precipitated from its solutions in acids by triple prus-
siate of potash
III. The base of zircon, or zirconium , is still unknown,
though investigated by Sir H. Davy in the same manner as
the base of silex. When potassium was brought into contact
with ignited zircon, potash was formed, and dark metallic
particles were diffused through the alkali.
SECTION VIII.
Glucine.
I. This earth was discovered by Vauquelin, in the year
1798. He obtained it from the aqua marina or beryl, a pre¬
cious stone of a green colour, and very considerable hardness,
which is found crystallized in Siberia. Glucine has since
been detected in the emerald of Peru, and in the gadolinite.
The following process may be employed to separate it from
the beryl :
Let the stone, reduced to a fine powder, be fused with
three times its weight of pure potash. To the fused mass add
a quantity of water, and afterwards diluted muriatic acid;
which last will effect a complete solution. Evaporate the
solution to dryness, re-dissolve the dry mass, and add carbo¬
nate of potash so long as any precipitation ensues. Dissolve
the precipitate in sulphuric acid ; add a little sulphate of pot¬
ash ; and, on evaporation, crystals of alum will be obtained.
By this process the alumine is detached. The residuary liquor,
which yields no more crystals, contains the glucine, and a
small portion of alumine. Add a solution of carbonate of
ammonia to excess; this will throw down the alumine, and
* Klaproth, ii, 214.
270
EARTHS#
CHAP. IX.
the glucine will remain dissolved by the superabundant carbo¬
nate. When this solution is evaporated to dryness, and mo¬
derately heated, the alkaline carbonate is expelled, and a car¬
bonate of glucine remains, in the proportion of 16 parts from
every 100 parts of the stone.
II. Glucine has the following properties :
1. It is a fine white and soft powder, resembling alumine
in its sensible properties ; and, like that earth, adhering to the
tongue. Its specific gravity is 2.97.
2. It has no action on blue vegetable colours.
3. It does not harden, or contract, like alumine, by heat ;
and is infusible.
4. It is insoluble in water, but forms with it a ductile paste.
5. It is soluble in liquid potash and soda, but not in the
solution of pure ammonia. In these respects it agrees with
alumine.
6. Glucine is soluble in carbonate of ammonia ; a property
distinguishing it from alumine.
7. It appears, like alumine, to have an affinity for colouring
matter.
8. With the different acids it forms combinations, which
have a sweet and rather astringent taste. Hence its name has
been derived from yTwxuc, signifying swreet.
9. It is not precipitated by triple prussiate of potash.
III. We have no knowledge of the base of glucine. When
obtained, its proper denomination will be glucinum . The
general fact of its existence is proved by igniting glucine with
potassium, which is thus changed into potash.
SECTION IX.
Yttria , or Ittria .
4
I. This earth was discovered in 1794, by Professor Ga-
dolin, in a stone from Ytterby in Sweden; and its title to the
character of a peculiar earth rests, also, on the unquestion¬
able authority of Klaproth and Vauquelin, both of whom
YTTRIA.
271
SECT. IX.
have made it the subject of experiment. The folding pro-
cess for obtaining it, is described by V auquelm m tiie o6tl
volume of the Annales tie Chimie , p. 150. _
Fuse the pulverized stone (called Gadolimte) in the manner
already described, with twice its weight of potash ; wash the
mass with boiling distilled water, and filter. The filtered
solution, which has a beautiful green colour, yields, timing
evaporation, a black precipitate of oxide of manganese. V. hen
this has ceased to appear, allow the liquor to stair , ‘team
the clear part, and saturate with nitric acid. Let the insolu¬
ble part be, also, digested with extremely dilute nitnc acid,
which will take up the soluble earths only, and will leave, un-
dissolved, the silex and oxide of iron. Let the two portions
be mingled together, and evaporated to dryness; then re-cis-
solved and filtered : by which means any remains of suex an
oxide of iron are separated. To obtain the yttria from the
nitric solution, it would be sufficient, if no other eart were
present, to precipitate it by carbonate of ammonia ; but sma
portions of lime, and of oxide of manganese, are still presem
alono- with it. The first is separated by a tew drops of cmbo-
„ate°of potash; and the manganese, by the cautious ana, non
of hydro-sulphuret of potash. The yttria is then to be pre¬
cipitated by pure ammonia, washed abundantly with watei,
and dried. It amounts to about 35 per cent, of the s„. •-
II Yttria has the following properties: .
1. It is perfectly white; but it is difficult to preserve it free
from a slight tinge of colour, owing to its contamination wit .
°teifhrsrtaste nor smell; and it is smooth to the
*"£ it^TwTin water, and infusible except by an in-
4, It is very ponderous ; its specific gravity being 4.842.
t I, i. no. a”, .eked b, P»e alk.lie. , and, in <b» ~P«,
it differs from glucine and alunnne, both of w ici are a
antly soluble in fixed alkalies.
6. Like glucine, it is soluble in carbonate of ammonia, bu
five or six times less so than that earth ; or, in other words, of
e,Ll quau.ide. Of glucine and Jttria, th. l*te, require* for
272
EARTHS.
CHAP. IX.
solution five or six times more of the carbonate of ammonia
than the former.
7. It is soluble in most acids ; and is precipitated by pure
alkalies, by barytes, and by lime.
8. From these solutions it is also precipitated by the oxalic
acid, and by oxalate of ammonia, in a state resembling fresh
precipitated muriate of silver. Prussiate of potash throws it
down in small white grains passing in a short time to pearl
grey ; phosphate of soda in a white gelatinous form ; and in¬
fusion of galls in brown flocculi.
9. Yttria, which has been a long time exposed to the action
of fire, gives out chlorine gas, when dissolved in common
muriatic acid; thus manifesting one property of a metallic
oxide *.
III. The base of yttria has not yet been exhibited in a se¬
parate form; but the presence of oxygen in yttria is esta¬
blished by its converting potassium into potash, when ignited
with that metal.
SECTION X.
Thorina.
I. While analyzing some minerals from the neighbour¬
hood of Fahlun in Sweden, Professor Berzelius found in them
a new earth, which he had also extracted, in the summer of
1815, from a species of gadolinite. In these it was combined
with the flu ate of cerium and yttria. The pulverized mineral
was first treated with concentrated sulphuric acid, which de¬
composed the greater part of it, and expelled the fluoric acid.
From this solution, sulphate of potash precipitated the oxide
of cerium, and caustic ammonia afterwards occasioned a far¬
ther precipitate. This, dissolved by long digestion in mu¬
riatic acid, consisted of the muriates of yttria and of the new
earth. It was evaporated to dryness, in order to expel the
excess of acid, and water poured over it to dissolve the mu¬
riate of yttria. The residue was subjected to the action of
* Nicholson’s Journal, xviii. 77.
5
SECT. X.
THORINA.
273
muriatic acid, and the solution accurately saturated by caustic
6 ammonia. On adding water, and applying a boiling heat, a
j white gelatinous precipitate fell, which was collected on the
1 filter. The liquor, that passed through the filter, was again
saturated with pure ammonia, and heated to ebullition, which
) occasioned a fresh precipitation of the same earth. This, when
washed and gently dried, is the substance in question.
II. 1. This earth, when dried, is perfectly white ; it ab-
3 sorbs carbonic acid, and dissolves with effervescence in acids.
l After calcination, its white colour remains unimpaired ; but
i if the heat has been strong, it is rendered less easily solu¬
ble in acids. The neutral solutions of it have a purely astrin¬
gent taste, which is neither sweet, nor saline, nor bitter, nor
metallic, a property in which it differs from all the earths ex¬
cept zirconia.
2. When dissolved in a slight excess of sulphuric acid, and
subjected to evaporation, it yields transparent crystals, which
are not altered by exposure to the air, and have a sweet astrin¬
gent taste.
3. It dissolves readily in nitric and muriatic acids, but does
not afford crystallizable salts. When precipitated by pure
alkalies, it absorbs carbonic acid from the air with avidity;
and the alkaline carbonates throw it down, in combination
with the whole of their carbonic acid. It is precipitated by
the oxalate, tartrate, and benzoate of ammonia. Succinate
of ammonia occasions a precipitate, which is immediately re¬
dissolved ; and ferro-prussiate of potash throws down a white
precipitate, which is soluble in muriatic acid.
4. It is not soluble, even when freshly precipitated and at a
boiling temperature, by the pure alkalies. The alkaline car¬
bonates dissolve it, but much more sparingly than any other
earth on which they are capable of acting.
5. It is not reducible, when strongly heated in contact with
charcoal. Before the blow-pipe, it cannot be brought into
fusion. With borax or phosphate of soda, it fuses into a
transparent glass, but is infusible with soda.
Messrs. Gahn and Berzelius having been accustomed to
speak of this earth under the name of Thorina (from Thor,
VOL. i. T
27 4
EARTHS.
CHAP. IX.
a Scandinavian deity), we may distinguish it by this name, till
a more appropriate one shall be pointed out.
Thorina differs from the other earths in the following pro¬
perties : From alumine and glucine , by its insolubility in liquid
potash ; from yttria , by its solutions being purely astringent
to the taste, without any sweetness, and by the property of
being precipitated at a boiling heat, except when prevented
by too great an excess of acid. It differs from zirconia in the
following respects : 1st, Because, after being ignited, it is still
soluble in acids. 2d, It is not precipitated by sulphate of pot¬
ash, which throws down zirconia, even from solutions con¬
taining a considerable excess of acid. 3d, Thorina is precipi¬
tated by oxalate of ammonia, which is not the case with zir¬
conia. 4th, Its combination with sulphuric acid crystallizes
readily, while sulphate of zirconia forms, when pure and
dried, a gelatinous transparent mass, without any trace of
crystallization.
V
CHAPTER X.
OF ACIDS IN GENERAL.
The term acid is applied to all bodies that possess one or
more of the following properties.
1. The acids have a peculiar taste, which is expressed in
common language by the term sourness. This is very dif¬
ferent, as to its degree, in different acids. In some it is so
intensely strong, that they cannot be applied to the tongue
without producing pain ; and it characterizes them, even when
diluted with several hundred times their weight of water.
The sourness of others is such only, as to render them agree¬
able to the palate.
2. The acids redden blue vegetable colours ; and they pos¬
sess this property even when very greatly diluted. Hence
blue vegetable infusions, or papers stained with them, become
tests of the presence of uncombined acids. A single drop of
sulphuric acid is capable of reddening a large quantity of water
coloured with litmus, or with syrup of violets.
3. The acids combine chemically with alkalies, earths, and
metallic oxides ; and totally destroy the peculiar qualities of
those bodies. Let a few ounce-measures of water be tinged
blue with syrup of violets ; add a few drops of solution of pot¬
ash, and the colour will be changed to green ; then drop in,
very slowly and cautiously, sulphuric acid much diluted, and
the blue colour will be restored. At this point, neither the
acid nor the alkali is in excess, as they are said to neutralize
each other ; and, on farther examination, it will be found that
the other characteristic qualities of the components have ceased
to be apparent in the compound.
It is not necessary, however, in order to entitle a body to
rank among the acids, that it should possess all the qualities
which have been enumerated. The prussic acid, for example,
is neither sour to the taste, nor does it redden blue vegetable
colours ; but yet, from its manifesting the properties of chemi-
t 2
276
OF ACIDS IN GENERAL.
CHAP. X,
cal combination, enumerated under the third head, it is ar¬
ranged among the acids. Other bodies, again, are excluded
(though perhaps improperly) from this class, which possess,
partly, the characters of acids. Thus sulphureted hydrogen
changes the blue colours of vegetables to red ; and combines
chemically with alkalies and earths.
All the acids were inferred by Lavoisier, from analogy with
those which had already been decomposed, to contain oxygen,
which was considered, by that distinguished philosopher, as
the general principle or cause of acidity. Since the brilliant
discoveries of Sir H. Davy, we may, with equal justice, con¬
sider oxygen as the general principle of alkalinity. And be¬
sides, it has been lately proved with respect to tellurium and
to the new substance iodine , and has been rendered highly
probable with respect to chlorine , that those bodies afford
acids, not only by uniting with oxygen, but also by com¬
bining with hydrogen. Sulphur, also, by combination with
hydrogen, acquires many characters of an acid; and a com¬
pound base of carbon and nitrogen, called cyanogen , has been
shown by Gay Lussac to form prussic acid by the addition of
hydrogen. The theory, therefore, that oxygen is essential to
acidity, must be abandoned. But it is still important to
know that most of the acids contain oxygen ; because it ex¬
plains many of their most interesting qualities, depending on
the transfer of oxygen from the acids to the bodies on which
they act.
The peculiar properties of each acid are derived from the
combustible base, with which the oxygen is united ; and so,
also, is its specific name. Thus sulphur, when oxygenated,
affords sulphuric acid ; carbon, carbonic acid ; and so of the
rest. But the same combustible base admits of being com¬
bined with different proportions of oxygen ; and the com¬
pounds, thus generated, are distinguished by a very different
train of qualities. Sulphur, for example, when combined
with the full proportion of oxygen, with which it is capable of
uniting, affords a very dense and corrosive acid, called the
sulphuric; when oxygenated in a less degree, it yields a pene¬
trating and suffocating gas called the sulphurous acid. By these
two terminations, the degrees of oxygenation are distinguish-
6
CHAP, X.
OF ACIDS IN GENERAL*
277
ed. Thus we have the phosphoric and phosphorous acids, the
nitric and nitrons ; the termination ic denoting an acid with
its full proportion of oxygen. In some cases, a combustible
base, which affords an acid when fully oxygenated, constitutes
only an oxide when combined with a less quantity of oxygen.
Carbon, for example, affords carbonous oxide and carbonic
acid, but, so far as is hitherto known, no intermediate product.
The following table exhibits the compounds, which result
from the oxygenation of some of the principal combustible
bases. It is introduced in this place, chiefly to show that the
oxygen in the more highly oxygenized compounds is in quan¬
tities, which are simple multiples of those in the less oxygen¬
ized compounds.
100 parts of united with Result.
oxygen . . carbonic acid,
i — — . . carbonous oxide.
> oxygen . . sulphuric acid.
1 * — — . . sulphurous acid.
1 — ■ — - . . persulphurous acid ?
oxygen . . nitric acid.
- . . nitrous acid.
- . . nitric oxide.
— - . . nitrous oxide.
oxygen . . phosphoric acid.
.5 - - . . phosphorous acid.
Carbon
Sulphur
Nitrogen . .
Phosphorus -<
265
132
150
100
50
285
228
114?
57
135
67
It is in consequence of the oxygen, which they contain, that
several of the acids are decomposed by inflammable substances,
with the disengagement of intense heat and light ; or that the
acids are (as they have been termed by Dr. Thomson) sup¬
porters of combustion . This property belongs most remarkably
to those acids, in -which oxygen is most weakly combined.
Thus the nitric acid retains its oxygen so feebly, that many
inflammable substances, when merely introduced into it at the
ordinary temperature of the atmosphere, take fire and burn
with vehemence. It is not, however, to be understood that
oxygen, and the compounds into which it enters, are the only
supporters of combustion ; for chlorine, iodine, and probably
fluorine, belong also to the same class of bodies.
278
or ACIDS IN GENERAL.
CHAP. X.
All acids in a solid or liquid state, it has been observed by
Berzelius, contain water as an essential element, and do not
abandon it without decomposition. Sulphuric and nitric
acids, for example, cannot exist independently of water. In
acids that are capable of assuming a solid form, water appears
to exist in two states, as a base essential to the constitution of
the acid, but yet incapable of neutralizing its acid properties ;
and as water of crystallization. Thus the citric acid in crys¬
tals contains 21 per cent, of water, of which only one third
can be expelled by heat without destroying the acid. A dif¬
ferent view, however, of this subject has been lately taken by
Dr. Murray #, who considers the oxygen and hydrogen in all
acids which are thus constituted as existing, not in the state of
water, but of ternary combination with the elements of the
acid, and as together conferring acidity. For example, liquid
sulphuric acid he regards not as a compound of real sulphuric
acid and water, but as a ternary compound of sulphur, oxy¬
gen, and hydrogen. Acidity, it would appear, therefore,
which is sometimes dependant on oxygen, and sometimes on
hydrogen, is in other cases (and those often of acids of a high
degree of intensity), the result of the combined operation of
the two principles.
Every acid, with a few exceptions, is capable cf uniting with
each individual of the classes of alkalies, earths, and metallic
oxides. In these compounds, the separate qualities of the com¬
ponent principles are in many instances no longer apparent,
and hence they have been called neutral salts. In every salt,
then, there are present two distinct ingredients. The acid, of
whatever kind it may be, has been denominated, by Lavoisier,
the salifying principle ; and the body, with which the acid is
combined, whether an alkali, an earth, or an oxide of any of
the common metals, the salifiable base , or simply the base. The
salts, formed by an individual acid with all these different
bases, maybe considered as a genus or class; and may be
distinguished by a generic name, expressive, in part, of their
composition. This generic name is taken from that of the
acid. The combination of sulphuric acid, for instance, wTith
* See bis paper on muriatic acid, Edinburgh Trans.
CHAP. X.
OF ACIDS IN GENERAL.
279
any base, is called a sulphat or sulphate ; of phosphoric acid a
phosphate ; and so of the rest. The name of the individual salt
is derived from that of the base. Thus we have the sulphat of
potash , the sulphat of soda, &c. But sulphur, phosphorus, and
other bodies, it has already been observed, are susceptible of
different degrees or stages of oxygenation; and afford, in
these different stages, acids which are characterized by a pe-
culiar train of properties. The compounds, also, which result
from the union of two different acids, having the same com¬
bustible base, with alkalies and earths, are altogether different
from each other. The salt, for example, which sulphuric acid
affords with potash, is wholly unlike that which results from
the combination of sulphurous acid with the same base. It
was necessary, therefore, to distinguish the compounds of the
more oxygenated from those of the less oxygenated acid ; and
this has been done by changing the termination from ate to
ite. Thus the salts, formed with sulphurous and phosphorous
acids, are called sulphites and phosphites ; as sulphite of pot¬
ash, phosphite of soda, &c.
An important law has been deduced, by Berzelius, respect¬
ing the combination of acids with bases, viz. that the quanti¬
ties of different bases , required to saturate a given quantity of
any acid , all contain the same quantity of oxygen. For example,
100 parts of sulphuric acid are saturated by a quantity of any
base, containing 20 parts of oxygen; and 1 00 parts of muri¬
atic acid by a quantity of base, which holds in combination
30.49 parts of oxygen. These proportions do not seem to be
changed by varying the state of oxygenation in the acid ; for
sulphites absorb oxygen to become sulphates, and still remain
neutral ; the phosphites, when changed into phosphates, give
up phosphorus, and continue neutral. It would appear, there¬
fore, that the proportion between the oxygen of the acid, and
that of the base, is regulated by the proportion of the com¬
bustible ingredients of the acid and base to each other. In
sulphurets, for example, the metal and sulphur are in such
proportion, that when both are oxygenated, the oxide, re¬
sulting from the one, precisely saturates the acid, resulting
from the other. These facts strongly confirm the atomic
theory, and cannot, indeed, be explained by any other.
280
OF ACIDS IN GENERAL.
CHAP. X,
Hitherto, v/e have considered the compounds of acids with
their respective bases only in the state of neutral compounds,
in which neither the acid, nor the base predominates. But
we have several instances, in which a neutral compound is
susceptible of uniting with an additional quantity of acid or of
base, and thus of acquiring an entirely new' set of properties.
Potash and tartaric acid, for example, wffien united in the
proportions which neutralize each other, compose an extremely
soluble salt, which has no action on vegetable colours ; but
with a double proportion of acid, a salt is formed, which requires
a large quantity of water for solution, has an acid taste, and
instantly reddens vegetable blue colours.
To distinguish this and other similar salts, the epithet acidu¬
lous was first proposed; but, for the sake of brevity, it has
now become customary to prefix the Latin preposition super .
Thus we have the .raper-tartrate of potash ; the super-sulphate
of potash ; &c. On the contrary, when the base is predomi¬
nant, we denote the deficiency of acid by the preposition sub,
as sub-carbonate of potash, sub-borate of soda, &c. In the
instance of the compounds of oxalic acid with potash, Dr.
Wollaston has employed the words binoxalate and quadrox -
alate, to express the proportions in which the acid unites with
the base ; and this method of nomenclature he has extended
to other salts, formed by the union of an acid and base in dif¬
ferent proportions. There are several cases, however, in which
it is extremely difficult to decide, whether a salt is to be classed
among neutral, or among sub or super salts
There are few instances of salts with compound bases ; and
in cases of this kind it is customary to annex to the generic
name those of both the bases. Thus, for example, we have
the tartrate of potash and soda, the phosphate of ammonia and
magnesia, or as it is sometimes called, ammoniaco-magnesian
phosphate.
In no part of chemistry is the advantage of the new nomen¬
clature more sensibly experienced, than in the class of neutral
salts ; for the number of these compounds is susceptible of
being multiplied to an immense extent. If the knowledge of
* See the remarks of Berzelius, Ann. de Chim. lxxix. 264, and lxxxii.
225.
CHAP. X. OF ACIDS IN GENERAL. 281
the name did not lead to that of the compound, scarcely any
memory would be adequate to retain them. But by changing
the arbitrary titles, formerly assigned to them, for names ex¬
pressive of their composition, we are furnished with a kind of
artificial memory, which renders their recollection perfectly
easy. Thus for the terms butter of antimony, sugar of lead,
and Glauber’s salt, are now substituted the more appropriate
epithets of muriate of antimony, acetate of lead, and sulphate
of soda.
4
Of those acids, which are supporters of combustion, a few
retain the same property even in combination. Nitrate of
potash, it is well known, enters into active inflammation with
charcoal, sulphur, and other combustible bodies. This is
owing to the quantity of oxygen which the nitric acid contains,
and which is less strongly attracted by the nitrogen than by
the newly added body.
Other properties, general to the class of salts, have already
been described in the section on cohesion ; especially their so¬
lubility, and their crystallization. On this last subject, it is
necessary to add the general law deduced by Berzelius, viz. that
in all salts, the water of crystallization contains a quantity of
oxygen either equal to that of the base ; or a multiplication of
it by 1, 2, 3, 4, &c. as far as 10; or a division by the same
numbers. In sub-carbonate of soda, and muriate of ammonia,
the quantity of oxygen in the water is equal to the oxygen in
the base ; in muriate of barytes, and in sulphates of ammonia
and lime, the oxygen of the water is double that of the base;
in green sulphate of iron, the oxygen of the water is seven
times that of the oxide of iron ; and, lastly, in carbonate and
phosphate of soda, it is ten times that of the base *.
The decrepitation of salts when suddenly heated, or expul¬
sion of water from them with noise, is owing probably to the
water being held not chemically but mechanically ; for it is
observed only in salts, which contain too small a quantity of
water, to allow its being considered as an essential element:
such as sulphate of potash, and muriate of soda.
The deliquescence of salts has been observed by Gay Lussac
* 80 Ann. de Chim, 187? note.
OF ACIDS IN GENERAL.
CHAP. X.
to bear a proportion to the temperature, at which saturated
solutions of the respective salts boil. The more deliquescent
the salt, the higher is the boiling point of its solution ; and if
not deliquescent at all, the boiling point of the solution is the
same as that of water
Having premised these general observations respecting the
acids and their compounds, I shall proceed to the history of
the different acids, and of the compounds which they yield
with the several alkaline and earthy bases. Under each head,
I shall first enumerate the properties of the base of the acid ;
and its combinations with such other combustible bodies, as
may already have been introduced to the reader's notice.
* 82 Ann. de Chim. 17 J.
/
CHAPTER XL
CARBONIC ACID AND ITS BASE.— -CARBONATES.— -BINARY COM¬
POUNDS OF CARBON.
The bodies, which form the subject of this chapter, will be
described in the following order : ,
I. Carbon, and its various modifications.
II. The compound of carbon and oxygen, in its highest
% stage of oxygenation, constituting carbonic acid ; and, con¬
nected with it, the class of salts called carbonates.
III. The oxide of carbon, or CARBONOTJS oxide, a com¬
pound containing less oxygen than exists in carbonic acid.
IV. The various combinations of carbon and hydrogen,
I termed carbureted hydrogen.
SECTION I.
Carbon and Charcoal .
It had long been admitted as an established truth, chieflv
on the evidence of the experiments of Guyton *, that the
diamond is the only form of pure carbon ; and that charcoal
is a compound of carbon and oxygen, or an oxide of carbon.
The important experiments of Messrs. Allen and Pepys have
suggested, however, that the diamond and charcoal, though
so widely remote from each other in external characters, are,
as to their chemical nature, identically the same; and that the
difference between them, in all probability, results merely
from the respective states of aggregation of their particles.
Some doubts, it must be confessed, were thrown on this
conclusion by an experiment of Sir H. Davy, in which an
inflammable gas was obtained, by igniting charcoal, in a To-
ricellian vacuum, by a powerful Voltaic battery. But the hy-
* Annales de Chimie, xxxi.
284
CARBON AND CHARCOAL.
CHAP. XI.
drogen, thus evolved, may reasonably be ascribed to water,
from which it is extremely difficult to free charcoal. The
absence of oxygen from charcoal was proved, by heating it
with potassium, for no potash was produced; but wrhen pot¬
assium was heated with diamond, there was an indistinct ap¬
pearance of the production of that alkali. The recent expe¬
riments of the same philosopher * tend to establish, that char¬
coal invariably contains either hydrogen or wxiter; for when
it is burned in pure and dry oxygen gas, some moisture is
always deposited. The quantity, however, is so small, that
hydrogen cannot exist in charcoal as an essential ingredient,
or in any definite proportion. The diamond appears to be
absolutely free both from water and hydrogen ; and it is in
this respect only, and in the mechanical arrangement of its
particles, that we have any evidence of its differing from char¬
coal. If proof were wanted of the identity of the two sub¬
stances, it is furnished by the fact that the diamond converts
iron into steel, under circumstances quite free from all sources
of fallacy f.
To obtain charcoal free from contamination, pieces of oak,
willow, hazle, or other woods, deprived of the bark, may be
buried in sand in a crucible, which is to be exposed, covered,
to the strongest heat of a wind-furnace. For purposes of ac¬
curacy, charcoal must be used when recently prepared, and
before it has had time to become cold ; or if it cannot be had
fresh made, it must be heated again to redness under sand in
a crucible.
A remarkably pure charcoal may be obtained, by passing
the vapour of oil of turpentine, or of spirit of wine, through
a red-hot tube. It then appears in the form of a black im¬
palpable powder. In the experiments of Sir II. Davy, this
sort of charcoal, by combustion in oxygen gas, gave a much
smaller product of moisture than any other.
From 100 parts of each of the following woods Messrs.
Allen and Pepys obtained the annexed quantities of charcoal ;
viz. from fir, 18.17; lignum vitae, 17.25; box, 20.25 ; beech,
15; oak, 17.40; mahogany, 15.75.
* Phil. Trans. 1814, p. 557.
f Phil. Trans. 1815, p. 371.
[i SECT. I.
CARBON AND CHARCOAL.
285
Charcoal has the following properties :
1. In its aggregated state it is black, perfectly insipid, and
i: free from smell; insoluble in water, brittle, and easily pul-
'i verized. In close vessels, and entirely secured from contact
with air, it is unchanged by any degree of heat. A gas, how-
4 ever, may be collected from it by distillation, which consists
c of hydrogen and carbon, and perhaps a little oxygen. Ber-
l: thollet has found, also, in the aeriform products of its distil-
jj lation, a considerable proportion of nitrogen *.
2. Charcoal has the singular property of absorbing gases
n without alteration. Fill a jar with common air, or any other
gas, and place it over dry mercury: take apiece of charcoal,
rj red-hot from the fire, and plunge it in the mercury of the
d bath : when cold, let it be passed into the vessel of gas, with-
o out bringing it into contact with the atmosphere. A consider-
i able diminution of the gas will be effected ; and in 24 or 36
d hours will be completed.
Count Morozzo has given the following table of the quan-
titles of different gases absorbed, in the foregoing manner,
A by charcoal. In each experiment, he employed a piece of
jj that substance 1 inch long and f of an inch diameter. The
i receiver containing gas was 12 inches long and 1 inch dia¬
meter.
)
L
>
L
[
>
Gas absorbed.
Atmospheric . .
Carbonic acid ......
Ammonia .
Muriatic acid .
Sulphureted hydrogen.
Inches .
. . 11
. . 11
.. 11
.. 11
Gas absorbed . Inches.
Nitrous . . 61-
Hydrogen . . 2-yL-
Oxygen . . . . . 2\-
Sulphurous acid . . 5^
Th is property of charcoal has been made the subject of a
ri valuable set of experiments by Saussure f. Charcoal of box-
r wood he found to absorb, of
Volumes.
Ammoniacal gas . . 90
Muriatic acid . % . . 85
Sulphurous acid . . . . . . . 65
Sulphureted hydrogen . 55
Nitrous oxide . . . 40
* Memoires cf Arcueil, ii, 484.
f Thomson’s Annals, vi. 241.
28 6
CARBON AND CHARCOAL.
CHAP. XI<
Volumes.
Carbonic acid . 35
Olefiant gas . . . . 35
Carbonic oxide. . . . . 9.42
Oxygen . . . . . . . 9.25
Azote . . . . 7.5
Hydrogen . . . 1.75
Most of the phenomena attending this absorption have'
already been described, in speaking (chap. v. sect, i.) of the
absorption of gases by solids. It appears to be entirely a me¬
chanical effect; for even those gases that have an affinity fore
charcoal (hydrogen and oxygen for instance), are given out
unchanged at the heat of boiling water. The densest and
heaviest kinds of charcoal are most remarkable for this pro¬
perty, which is much diminished by pulverizing them ; and
does not exist at all in plumbago or in stone coal.
3. From the experiment of Rouppe#, it appears, that if
charcoal, which has imbibed oxygen gas, be brought into)
contact with hydrogen gas, water is generated ; but Saussure, .
hy a careful repetition of it, could not obtain the same result.
4. Charcoal, by long exposure to the atmosphere, absorbs \
one twentieth of its weight, three fourths of which are water f. .
The charcoal of different woods, Messrs. Allen and Pepys >
found to increase very differently in weight ; that from fir •
gaining, by a week’s exposure, 13 per cent. ; that from lignum i
vitae, in the same time, 9.6; from box, 14; beech, 16.3; oak,,
16.5; mahogany, 18. The absorption goes on most rapidly
during the first 24 hours; and by much the largest part of
what is absorbed consists of water merely.
5. Charcoal resists the putrefaction of animal substances.
A piece of flesh-meat, which has begun to be tainted, may
have its sweetness restored by rubbing it daily with powdered
charcoal ; and may be preserved sweet for some time by bury¬
ing it in powdered charcoal, which is to be renewed daily.
Putrid water is also restored by the application of the same
substance ; and water may be kept unchanged at sea, by char-
rum the inner surface of the casks which are used to contain
* Ann. de China, xxxii. 1.
f Clement and Desormes.
SECT. II.
COMBUSTION OF CARBON.
287
it It produces, also, a remarkable effect in destroying the
taste, odour, and colour of many vegetable and animal sub¬
stances. Common vinegar, by being boiled on it, is rendered
perfectly limpid. Rum and other varieties of ardent spirit,
which are distinguished by peculiar colours and flavours, lose
both by maceration with powdered charcoal. The colour of
litmus, indigo, and other pigments, dissolved or suspended in
water, is destroyed. Putrid animal fluids, and air contami¬
nated with offensive fumes, are, also, completely deprived of
i their odour. These effects are most readily produced by ani-
i mal charcoal f .
6. Charcoal is a very slow conductor of caloric. The ex¬
periments of Guyton have determined, that caloric is conveyed
through charcoal more slowly than through sand, in the pro¬
portion of three to two. Plence powdered charcoal may be
advantageously employed to surround substances which are to
be kept cool in a warm atmosphere; and also to confine the
caloric of heated bodies.
7. The weight of the atom of charcoal is inferred by Mr.
Dalton to be 5.4, that of oxygen being 7. But if the weight
of the atom of oxygen be corrected to 7.5, the atom of char¬
coal will then weigh 5.8. The evidence in favour of this con-
) elusion will be stated in the following section. The specific
i gravity, which it would have, if reducible into a vaporous
t form, is calculated by Gay Lussac to be 0.4*16.
SECTION IL
Combustion of Carbon.
If a small piece of charcoal be exposed red-hot to the com¬
mon atmospheric air, it exhibits scarcely any signs of com¬
bustion, and soon becomes cold. Sir H. Davy has indeed
lately observed that dry charcoal converts oxygen gas pretty
rapidly, though imperceptibly, into carbonic acid, if kept at
* Lovitz, Ann. de China, tom. xiv.
f 79 Ann. de China. 80 ; Journ. of Science, &c, iv. 367 ,
288
COMBUSTION OF CARBON.
CHAP. XI.
a temperature a little above the boiling point of quicksilver *.
And if a piece of charcoal, heated to about 800° or 1000°
Fahrenheit, or nearly to redness, be introduced into a receiver
filled with oxygen gas, it continues to burn with greatly in¬
creased splendour, and with bright scintillations. If the
charcoal be pure, and its proportion rightly adjusted, it is en¬
tirely consumed. When the quantity burnt is considerable,
a manifest production of water takes place, and the inner sur¬
face of the glass vessel becomes covered with moisture, which
disappears, however, on standing. This portion of water
owes its origin to the union of oxygen with the hydrogen
which, it appears from Sir II. Davy’s experiments, and from
the results of its distillation, all charcoal contains.
The diamond, also, which was formerly considered as an
incombustible substance, may be consumed by a sufficiently
intense heat, even in atmospherical air. The Florentine aca¬
demicians, in the year 1694, appear first to have ascertained
this fact, by exposing diamonds to the focus of a powerful
burning lens. Their experiment has been repeated by subse¬
quent chemists, with various modifications. It has been found
by Sir George Mackenzie that diamonds burn, when exposed
on a muffle, to the temperature of about 14° Wedgwood. In
oxygen gas the diamond takes fire, when the focus of a power¬
ful lens is thrown upon it; and continues to burn, though
removed out of the focus, with a steady brilliant light, visible
in the strongest sunshine f. The portion of diamond, which
remains unconsumed, is not rendered black, as has been
asserted, but is found to have lost its lustre, like glass acted
on by fluoric acid. When the vessel has become cold, no
production whatsoever of moisture is visible. By effecting its
combustion in this way, Guyton thought he had determined
that the diamond, in an equal weight, contains more real
carbon than exists in common charcoal. Flis experiments,
however, have not been confirmed by those of subsequent
chemists. One fact, however, has been contributed on this
# _
subject by Guyton, which is of considerable value. The dia-
* Phil. Trans. 1817, p. 16.
+ Davy, in Phil. Trans. 1814.
SECT. II.
COMBUSTION OP CARBON.
289
mond, he first ascertained, is destroyed when thrown into
red-hot and melted nitre ; and this property, it will afterwards
appear, has been successfully applied by Mr. Tennant to the
determination of the nature of the diamond, and of the pro¬
portion of ingredients in carbonic acid.
To collect the products of the combustion of carbon, re¬
quires rather a complicated apparatus. Lavoisier burnt char¬
coal in a known quantity of oxygen gas, .which was confined
by mercury, the charcoal being set on fire by a bent iron wire
heated to redness *. Messrs. Aden and Pepys collected the
products of the combustion of charcoal and of the diamond,
by burning them separately in a platinum tube, set horizon¬
tally in a charcoal furnace, and connected, at each extremity,
with a mercurial gazometer. An idea of this arrangement
will best be obtained by imagining that to each end of the
tube c, fig. 40, the pipe b of a gazometer, like that shown fig.
35, is connected. At the outset of the experiment, one of
\ the gazometers was filled with a known quantity of the purest
oxygen gas, and the other was empty. The tube was then
made red-hot ; and the gas, being forced alternately from one
gazometer to the other, was repeatedly brought into contact
with the red-hot charcoal or diamond. The volume of the
gas was found to be entirely unaltered ; but it had received an
addition to its weight, precisely equal to what the charcoal of
diamond, on weighing, was ascertained to have lost; and it
was partly converted into a gas, totally different in its pro¬
perties from oxygen gas, and called carbonic acid. It ap¬
pears, therefore, that oxygen gas, by conversion into carbonic
acid, undergoes neither expansion nor condensation. This
conclusion is farther established by the recent experiments of
Sir H. Davy, on the combustion of the diamond in oxygen
gas.
* Elements of Chemistry, pi. iv„ fig. 3.
w
VOL. I.
CARBONIC ACID.
CHAP. XI.
290
SECTION III.
Carbonic Acid .
From the quantity of charcoal or diamond consumed in the
experiments of Allen and Pepys, and the quantity of oxygen
converted into carbonic acid, it is easy to infer the proportion
of carbon and oxygen in the new compound. Reducing these
to centesimal proportion, for every 28 or 29 grains of the
combustible base which disappeared, 100 grains of carbonic
acid (= about 201 cubic inches) were generated; and it is
remarkable that these proportions agree exactly with those
originally stated by Lavoisier. The same quantity of carbonic
acid resulted, also, from the combustion of between 28 and
29 grains of diamond. Hence it may be inferred, that the
actual quantity of carbon in equal weights of diamond and
charcoal is precisely the same ; and that charcoal is not, as
has hitherto been supposed, an oxide of carbon. If this in¬
ference required confirmation, it is furnished by its agreement
with Mr. Tennant’s experiments on the combustion of the
diamond, published in 1797. Two grains and a half of dia¬
mond (this philosopher found), when consumed in a tube of
gold by means of nitre, gave nine grains of carbonic acid,
which, in 100 parts should contain, therefore, as nearly as
possible, 28 parts of diamond or carbon. The mean of a
number of Messrs. Pepys and Allen’s experiments give the
following statement of the composition of carbonic acid :
Carbon . 28.60 . 100
Oxygen ......... 71.40 . 250
100.
It is remarkable, also, that these numbers are precisely
those, which result from the experiments of Clement and
Desormes *. They differ, however, a little, from those of
Saussure, jun., who states the carbon in 100 grains of carbonic
ficid at between 27.04 and 27.38 grains. The results of Gay
* Ann. de Chim. x,xxix. 42.
SECT. III. CARBONIC ACID. 291
Lussac, which are conformable with the views of Berzelius*
and, as nearly as possible, with those of Dr. Wollaston, are,
Carbon . ...... 27.376 . 100 . 37.55
Oxygen . . 72.624* . . 265.12 . . 100.
100. 365.12 137.55
Mr. Dalton assumes the composition of carbonic acid to be,
in round numbers, 28 of charcoal and 72 of oxygen ; from
4 whence he deduces the weight of the atom of charcoal to be
5 5.4. But if the atom of oxygen weigh 7.5, and if the pro-
d portions of Gay Lussac be correct, the atom of charcoal will
w weigh 5.65, and that of carbonic acid (considering it as a ter-
d nary compound of two atoms of oxygen and one of charcoal)
i will be 20.65.
In addition to the proofs of the constitution of carbonic
e acid, derived from its synthesis, we have also the evidence of
ti its analysis, which may be effected by several processes.
1. By passing a succession of electrical discharges through
v a quantity of carbonic acid gas confined over mercury, I have
i found that the gas is separated into oxygen, and a gas called
i carbonous oxide, which consists of oxygen united with a
larger proportion of carbon, than exists in carbonic acid.
r When the carbonic acid, which escapes decomposition, is
1 washed out by solution of potash, an electric spark inflames
i the residuary mixture ; the oxygen and carbonous oxide again
a uniting, and re-composing carbonic acid *.
2. When a mixture of carbonic acid and hydrogen gases is
a electrified, the hydrogen combines with part of the oxygen in
1 the acid, and reduces it to the state of carbonous oxide.
3. WThen potassium is heated in carbonic acid gas, Sir XL
Davy has found that it inflames ; part of it is oxidated at the
i expense of the acid ; and part of it unites with the charcoal,
which is precipitated.
4. By simply heating phosphorus in carbonic acid gas, no
step is made towards the decomposition of the latter. But
by applying phosphorus to some of the combinations of car¬
bonic acid, the phosphorus is oxygenated, and carbon appears
* Phil. Trans. 1809, p. 448.
u 2
292
CARBONIC ACID.
CHAP. XI.
in a separate form. The original discovery of this fact is due
to Mr. Tennant* *, and the details of the experiment have
been ably followed up by Dr. Pearson f .
To exhibit this fact, provide a tube of very thin glass, about
one third of an inch wide, and 18 or 20 inches long, sealed
at one end. Coat it, within about an inch of the sealed ex¬
tremity, with a lute of sand and clay ; and when this is dry,
put into it as much purified phosphorus, in small pieces, as
will fill the uncoated part. Then cover the phosphorus with
carbonate of lime, or carbonate of soda which has been de¬
prived of its water of crystallization. Let the part of the tube,
which contains the carbonate, be made red-hot by means of a
portable furnace ; and, at this moment, apply heat to the part
containing the phosphorus, sufficient to melt and raise it into
vapour. The vapour of the phosphorus, coming into contact
with the red-hot carbonate, will decompose the carbonic acid;
and charcoal will be found in the residue of the process, in
the form of a very light and black powder.
To procure carbonic acid, sufficiently pure for the exhibi¬
tion of its properties, the combustion of charcoal is far from i
being the best process. The student may, therefore, have
recourse to another, the rationale of which he will not, at
present, understand ; but which will be explained afterwards, j
Into ax common gas bottle, put a little powdered marble or
chalk, and pour on this sulphuric acid, diluted with five or
six times its weight of water. A gas will be produced, which
those, who have an opportunity, may receive over mercury ;
but a mercurial apparatus is not absolutely essential, since the
gas may be collected over water, if used immediately when
procured. Carbonic acid may, also, be separated by heat
alone, from carbonate of lime. For this purpose, coarsely
powdered chalk or marble may be put into the iron vessel u,
fig. 85, which may be connected, by means of the conducting
pipe 5, with a gazoraeter. The receiving cylinder of the latter,
after a sufficiently long continuance of heat to the bottle a ,
will be filled with carbonic acid gas. Its properties are the
following :
o
— . - ■ — - ■ ■ — ■— — — ■ ■. — - . . — . — -- — — -- — —
* Phil. Trans. 1791, p. 182.
t Ibid. 1792, p. 289.
CARBONIC ACID.
293
SECT. III.
Properties of Carbonic Acid .
(a) It extinguishes flame. — Set a vessel, filled with the gas,
with its mouth upwards, and let down a lighted candle. The
candle will instantly be extinguished.
A person, says Dr. Priestley, who is quite a stranger to the
i properties of this kind of gas, will be agreeably amused with
extinguishing lighted candies, or blazing chips of wood, on
ii its surface. For the smoke readily unites with this kind of
i air; so that little or none of it escapes into the atmosphere.
It is remarkable, that the upper surface of this smoke, floating
in the fixed air, is smooth and well defined ; whereas the
Slower surface is exceedingly ragged, several parts hanging
down to a considerable distance within the body of the car¬
bonic acid, and sometimes in the form of balls, connected to
the upper stratum by slender threads, as if they were sus-
; pended. The smoke is also apt to form itself into broad
$ flakes, exactly like clouds. Making an agitation in this air,
3 the surface of it (which still continues exactly defined) is
thrown into the form of waves ; and if, by this agitation, any
of the carbonic acid be thrown over the sides of the vessel,
i the smoke, which is mixed with it, will fall to the ground, as
i if it were so much water.
(b) It is fatal to animals. — Put a mouse, or other small
. animal, into a vessel of the gas, and cover the vessel, to pre-
r vent the contact of common air. The animal will die in the
i course of a minute or two.
By means of this gas, butterflies, and other insects, the
colours of which it is desirable to preserve, for the purpose
of cabinet specimens, may be suffocated better than by the
common mode of killing them with the fumes of sulphur.
(c) This gas is heavier than common air. — According to Sir
H. Davy, 100 cubic inches, at 55° Fahrenheit, and 30 inches
of the barometer, weigh 47. 5 grains: and at 60°, with the
same pressure, w7ould weigh 47.11. Messrs Allen and Pepys
have lately determined that J 00 cubic inches, at 60° Fahren¬
heit, and 30 inches barometer, weigh 47.26 grains. Its spe¬
cific gravity, according to Biot and Arajo, is 1.5196; and
hence, if 1G0 cubic inches of atmospheric air weigh 30.5
294
CARBONIC ACID.
CHAP. XI.
grains, the same bulk of carbonic acid gas should weigh
46.34 grains; Dr. Ure finds it to be 46.4. It will be a suffi¬
ciently near approximation to state the weight of 100 cubical
inches to be 47 grains, at a mean of the barometer and ther¬
mometer.
To show the superior specific gravity of this gas in a general
way, the following experiment will be sufficient. Let a long
glass tube, proceeding from a gas bottle, containing pow¬
dered marble and dilute sulphuric acid, be twice bent at right
angles ; let the open end of the longer leg reach the bottom
of a glass jar, perfectly dry within, and standing with its
mouth uppermost. The carbonic acid will expel the common
air from the jar, because it is heavier. — This superior gravity
may be farther shown as follows : When the jar is perfectly
filled with the gas (which may be known by a lighted candle
being instantly extinguished when let down into it), take
another jar, of rather smaller size, and place at the bottom
of it a lighted taper, supported by a stand : then pour the
contents of the first-mentioned jar into the second, as if you
were pouring in water. The candle will be instantly extin¬
guished, as effectually as if it had been immersed in water.
It is owing to its superior gravity, that carbonic acid gas is
often found at the bottom of deep wells and of mines, the
upper part of which is entirely free from it. Hence the pre¬
caution, used by the sinkers of wells, of letting down a candle
before they venture to descend in person.
( d ) Carbonic acid gas is absorbed by water. — Fill partly a
jar with this gas, and let it stand a few hours over water. An
absorption will gradually go on, till at last none will remain.
Th is absorption is infinitely quicker when agitation is used.
Repeat the above experiment, with this difference, that the
jar must be shaken strongly. A very rapid diminution will
now take place. In this manner water may be charged with
rather more than its own bulk of carbonic acid gas ; and it
acquires, when thus saturated, a very brisk and pleasant taste.
This impregnation is most commodiously effected by an appa¬
ratus, sold in the glass shops, under the name of Nooth’s
machine.
The influence of pressure, in occasioning water to absorb
SECT. III.
CARBONIC ACID.
a large quantity of carbonic acid, may be illustrated by an
apparatus, which I have described in the Philosophical Trans¬
actions for 1803, but which cannot be understood without the
engraving that accompanies it. From a long series of expe¬
riments with this apparatus, I have deduced, as a general
law, that water takes up the same volume of compressed car¬
bonic acid gas, as of gas under ordinary pressure. And since
the space occupied by any gas, is inversely as the compressing
force, it follows that the quantity of gas, forced into water,
is directly as the pressure. Thus, if water under common
3 circumstances takes up an equal bulk of carbonic acid, under
the pressure of two atmospheres, it will absorb twice its bulk ;
under three atmospheres three times its bulk, and so on.
(e) From water , thus impregnated , carbonic acid is again set
ai liberty , on boiling the water , or by exposing it under the re¬
ceiver of an air-pump . — During exhaustion, the gas will escape
so rapidly, as to present the appearance of ebullition; and
will be much more remarkable than the discharge of air from
a jar full of common spring water, confined, at the same time,
under the receiver, as a standard of comparison.
(f) Carbonic acid is expelled from water by freezing. — If the
impregnated water be rapidly congealed, by surrounding it
with a mixture of snow and salt, the frozen water has more
the appearance of snow than of ice, its bulk being prodigiously
increased by the immense number of air bubbles. When
water, thus congealed, is liquefied again, it is found, by its
taste, and other properties, to have lost nearly the whole of
its carbonic acid.
(g) Carbonic acid gas , when combined with water , reddens
vegetable blue colours. — This may be shown by dipping into
water, thus impregnated, a bit of litmus paper, or by mixing,
with a portion of it, about an equal bulk of the infusion of
litmus. This fact establishes the title of the gas to be ranked
among acids. When an infusion of litmus, which has been
thus reddened, is either heated, or exposed to the air, its blue
colour is restored, in consequence of the escape of the car¬
bonic acid. This is a marked ground of distinction from most
■ other acids, the effect of which is permanent, even after boiling.
(Ji) Carbonic acid gas precipitates lime water . — This character
296
CARBONIC ACID.
CHAP. XI
of the gas is necessary to be known, because it affords a ready
test of the presence of carbonic acid whenever it is suspected.
Pass the gas, as it proceeds from the materials, through a
portion of lime water. This, though perfectly transparent
before, will instantly grow milky : Or, mix equal measures of
water saturated with carbonic acid and lime water. The
same precipitation will ensue. By means of lime water, the
whole of any quantity of carbonic acid, existing in a mixture
of gases, cannot, however, be removed, as Saussure jun.
has shown ; but recourse must be had, in order to effect its
entire absorption, to a solution of caustic potash or soda.
(i) By the application of the test (It) it will be found , that
carbonic acid is generated in several cases of combustion. — 1. Let
the chimney of a small portable furnace, in which charcoal is
burning, terminate, at a distance sufficiently remote to allow
of its being kept cool, in the bottom of a barrel provided
with a moveable top, or of a large glass vessel having two
openings. A small jar of lime water being let down into the
tub or vessel, and agitated, the lime water will immediately
become milky. The gas will also extinguish burning bodies,
and prove fatal to animals that are confined in it. Hence the
danger of exposure to the fumes of charcoal, which, in several
instances, have been known to be fatal. These fumes consist
of a mixture of carbonic acid and nitrogen gases with a very
small proportion of oxygen gas. 2. Fill the pneumato-che-
xnical trough with lime water, and bum a candle, in a jar
filled with atmospheric air, over the lime water till the flame
is extinguished. On agitating the jar, the lime water will
become milky. The same appearances will take place, more
speedily and remarkably, if oxygen gas be substituted for
common air. The carbonic acid, thus formed during com-
bustion, by its admixture with the residuary air, renders it
more unfit for supporting flame, than it otherwise would be
from the mere loss of oxygen. Hence, if a candle be burnt
in oxygen gas, it is extinguished long before the oxygen is
totally absorbed, because the admixture of carbonic acid with
oxygen gas, in considerable proportion, unfits it for support¬
ing combustion. Whenever any substance, by combustion in
oxygen gas or common air over lime water, gives a precipi-
SECT. III.
CARBONIC ACID.
297
tate, soluble with effervescence in muriatic acid, we may con¬
fidently infer that it contains carbon.
(k) The respiration of animals is another source of carbonic
acid. — On confining an animal in a given portion of atmo¬
spheric air, over lime water, this production of carbonic acid
is evinced by a precipitation. The same effect is also pro¬
duced more remarkably in oxygen gas. The production of
carbonic acid, by respiration, may be proved, also, by blow¬
ing the air from the lungs, with the aid of a quill, through
lime water, which will immediately grow milky. The car¬
bonic acid, thus added to the air, unfits it for supporting life,
not merely by diminishing the proportion of oxygen gas, but
apparently by exerting a positively noxious effect. Hence a
given quantity of air will support an animal much longer,
when the carbonic acid is removed as fast as it is formed, than
when suffered to remain in a state of mixture. It has been
found, that an atmosphere, consisting of oxygen gas and
carbonic acid, is fatal to animals, though it should contain a
larger proportion of oxygen than the air we commonly breathe.
(/) Carbonic acid is at all times present in the air of the at¬
mosphere.— This might naturally be expected from the im¬
mense quantity which is constantly produced by respiration
and combustion. Its presence is demonstrated by leaving a
shallow vessel of lime water exposed to the atmosphere; for its
surface is soon covered with a solid pellicle, which, when re¬
moved, is succeeded by another, and so on, till the water is
deprived of all the lime, which it held in solution. From the
precipitate, thus formed, carbonic acid is disengaged by dilute
acids.
The quantity of carbonic acid, present in atmospheric air,
is estimated by Mr. Dalton not to exceed one thousandth of
its bulk. Saussure examined its proportion in the air of an
open field, a few miles from Geneva In January, the mean
of three experiments showed 4.79 parts in 10,000; in July
and August, 7.18 parts in the same volume, which is even con¬
siderably short of the small proportion determined by Mr.
Dalton. The difference between the quantities discovered in
* Ann. de Chim, et Phys. ii. 199; andiii. 170.
29$
CARBONIC ACID.
CHAP. XI.
summer and winter, though on first view very small, viz. 2-^
volumes in ten thousand, would constitute so large a quantity,
when the whole atmosphere is taken into the account, that
the fact can scarcely be considered as determined without re¬
peated and careful experiments.
(m) Carbonic acid retards the putrefaction of animal sub¬
stances . — This may be proved, by suspending two equal pieces
of fiesli meat, the one in common air, the other in carbonic
acid gas, or in a small vessel through which a stream of
carbonic acid is constantly passing. The latter will be
preserved untainted some time after the other has begun to
putrefy.
( n ) Carbonic acid gas exerts powerful effects on living vege¬
tables. — These effects, however, vary according to the mode
of its application.
Water, saturated with this gas, proves highly nutritive,
when applied to the roots of plants. The carbonic acid
is decomposed, its carbon forming a component part of
the vegetable, and its oxygen being liberated in a gaseous
form.
On the contrary, carbonic acid, when a living vegetable is
confined in the undiluted gas over water, is injurious to the
health of the plant, especially in the shade. The late Mr.
Henry, however, long ago found that a certain quantity of
fixed air, applied as an atmosphere, is favourable to vegeta¬
tion ; and M. Saussure, of Geneva, has determined more re¬
cently, that the mixture of more than ± of carbonic acid -with
common air is always injurious; but that in this proportion it
promotes the growth of plants, and is manifestly decomposed.
Carbonic acid is susceptible of combination with alkalies,
earths, and metals, and forms an order of compounds, termed
carbonates. At present, however, we shall only attend to the
results of its union with alkalies, and earths. In the com¬
pounds of carbonic acids with these bases, and especially with
the alkalies, the qualities of the base still predominate. The
alkaline carbonates, for example, retain the taste, though in
a less degree, which characterizes their bases; and change
blue vegetable colours to green. Ammonia, also, preserves in
6
SECT. IV.
CARBONATES.
299
a great measure its odour and volatility. By combination
with the earths, however, carbonic acid produces a more per¬
fect neutralization of their properties.
SECTION IV.
Carbonates .
Art. I. — Sub-carbonate , and Bi-carbonate of Potash,
(a) Carbonic acid gas is very abundantly absorbed by a solution
of pure potash. — The simplest mode of showing this fact is the
following : Fill a common phial with carbonic acid gas over
r water ; and when full, stop it by applying the thumb. Then
i invert the bottle in a solution of pure potash, contained in a
cup, and rather exceeding in quantity what is sufficient to fill
| the bottle. The solution will rise into the bottle, and,' if the
i gas be pure, will fill it entirely. Pour out the alkaline liquor,
{ fill the bottle with water, and again displace it by the gas.
Proceed as before, and repeat the process several times. It
will be found, that the solution will condense many times its
bulk of the gas ; whereas water combines only with its own
volume. ,
This experiment may be made, in a much more striking
manner, over mercury, by passing into a jar, about three
fourths filled with this gas, a comparatively small bulk of a
solution of pure potash, which will condense the whole of the
gas. If dry potash be substituted in this experiment, no
change will ensue ; which proves, that solution is essential to
the action of alkalies on this gas.
One hundred grains of potash unite with 42.42 carbonic
acid to form the sub-carbonate, which, therefore, contains
per cent, according to Berard,
Potash ........ 70.21
Acid . . 29.79
100.
The composition of this salt is differently stated by other
writers, viz .
CARBONATES.
300
CHAP. XI.
Acid. Base.
According to Dalton 100 grains consist of 31.10 . .68.9
• - - - Dulong . . . 30.70 . .69.30
• — . - Dr, Wollaston . . 31.71 . .68.29
- — — - Vauquelin . 33. . .67.*
The proportions of 70 to 30 agree very nearly with the
notion, that the sub-carbonate of potash is constituted of an
atom of carbonic acid, weighing 20.8, and an atom of potash
weighing 50; and that the weight of its atom is 70.8. The
affinity of carbonic acid for potash, though apparently feeble,
is in reality very strong ; since it has the power of expelling,
from potash, the whole of the water, which that alkali con¬
tains in the state of a hydrate.
(5) The changes effected in the alkali may next he examined. — *
It will be found, after having absorbed as much carbonic acid
as it is capable of condensing, to have lost much of its cor¬
rosive and penetrating taste, and will no longer destroy the
texture of woollen cloth ; but it still turns to green the blue
infusion of vegetables. Before its absorption of this gas, no
remarkable change ensued on mixing it with diluted sulphuric
acid ; but if this, or almost any other acid, be now added, a
violent effervescence will ensue, arising from the escape of the
gas that had been previously absorbed. If the mixture be
made in a gas bottle, the gas, that is evolved, may be col¬
lected, and will be found to exhibit every character of car¬
bonic acid.
For experimental purposes, sub-carbonate of potash may
be obtained from crystals of tartar (super-tartrate of potash)
calcined in a crucible ; then lixiviated with water ; and eva¬
porated to dryness. By this treatment, the salt yields about
one third its weight of sub-carbonate. Or it may be mixed
with about an eighth of purified nitrate of potash, and
wrapped up in paper in the form of cones, which may be
placed on an iron dish, and set on fire. The residuary mass
is to be lixiviated, and evaporated as before directed. Or
purified nitrate of potash may be mixed with a fourth of its
weight of powdered charcoal, and projected into a red-hot
* Ann. de Chim. et Phys/v. 25.
I SECT. iv. SITB-CARBONATE OF POTASH. 301
crucible, the contents of which are to be poured, when in
1 fusion, into an iron dish. The sub-carbouate, thus obtained*
i amounts to rather less than one half the nitre which has been
employed. Even when thus prepared, it is apt to contain
i some impurities, consisting chiefly of a minute proportion of
sulphate and muriate of potash, with a little silex, from which
it is extremely difficult entirely to free it. That which is pro¬
cured from burnt tartar may be made to crystallize, in which
? state it contains 20.60 per cent, of water.
(c) In this state of sub-saturation with carbonic acid, potash
generally occurs in the arts. The potash and pearlash of
i commerce, are sub-carbonates of potash, of different degrees of
| purity. The quantity of carbonic acid, contained in these al¬
kalies, may be learned by a very simple experiment. Put one
» or two hundred grains of the alkali into a Florence flask, and
s add a few ounce-measures of water. Take also a phial filled
with dilute sulphuric acid, and place this, as well as the flask,
in one scale. Balance the two, by putting weights into the
opposite scale, and, when the equilibrium is attained, pour
gradually the acid into the flask of alkali, till an effervescence
no longer ensues. When this has ceased, the scale containing
t the weights will be found to preponderate. This shows that
the alkali, by combination with an acid, loses considerably of
its weight ; and the exact amount of the loss may be ascer¬
tained, by adding weights to the scale containing the flask
; and phial, till the balance is restored.
(d) As it is sometimes of importance to know what propor¬
tion of real alkali a given weight of potash or pearlash con¬
tains, it may be proper to point out how this information may
be acquired. I shall, therefore, in Part III. Chap. III. of this
work, describe at length the apparatus and process best
adapted to this purpose.
(e) Sub-carbonate of potash dissolves very readily in water ,
tuhich , at the ordinary temperature , takes up more than iis own
weight. — -Hence, when an alkali, which should consist almost
entirely of sub-carbonate of potash, is adulterated, as very
often happens, with substances of little solubility, the fraud
may be detected by trying how much of one ounce will dis¬
solve in two or three ounce-measures of water. In this way I
SO 2
CARBONATES.
CHAP. XI,
have detected an adulteration of one third its weight of sul¬
phate of potash. There are certain substances of ready solu¬
bility, however, which may be used in adulterating pearl-
ashes, as common salt for example ; and, when this is done,
we must have recourse to the acid test for the means of dis¬
covery.
The strongest solution of this salt that can be obtained has
the specific gravity 1.54, and contains 48.8 per cent, by weight,
or eight atoms of water to one of salt.
(f) Sub-carbonate of potash, when exposed to the atmo¬
sphere, attracts so much moisture, as to pass rapidly to a li¬
quid state. This change is termed deliquescence. All the water
thus absorbed is expelled again by a heat of 280°.
(g) When submitted, in a crucible, to a high temperature,
it fuses ; but none of its carbonic acid is expelled.
Bi-carbonate of Potash.
Carbonate of potash, in the state which has been already
described, is far from being completely saturated with acid.
This sufficiently appears from its strongly aikaline taste. It
may be much more highly charged with carbonic acid, by ex¬
posing a solution of one part of the sub-carbonate in three of
water to streams of carbonic acid gas, in a Nooth’s machine, or
other apparatus ; or by the process to be described in art. 3, g .
When a solution of alkali, after this treatment, is very
slowly evaporated, it forms regular crystals. According to Dr.
Wollaston *, the quantity of acid in the bi-carbonate is exactly
double that in the sub-carbonate. This he proves by disen¬
gaging the carbonic acid from each, by a stronger acid, such
as the sulphuric. One part of the bi-carbonate, thus treated,
is found to give twice as much carbonic acid as the sub-salt.
Berthollet f obtained 189 grains of carbonic acid from 500 of
this salt ; and as nearly as possible, the same quantity from
1000 grains of the salt, reduced by calcination to sub-carbo¬
nate. Berat'd found, that 1 00 parts of potash are fully satu¬
rated by 85.86 carbonic acid J. The following Table exhibits
* Philosophical Transactions, 1808. f Mem. d’Arcueil, ii. 470.
t 71 Ann. de Chim. 42.
\
SECT. IT.
BI-CARBONATE OF POTASH.
305
the composition of the bi-carbonate, as stated by him, and by
i Dr. Wollaston. One hundred grains contain,
According to Berard .
Dr. Wollaston
Vauquelin . . . .
Acid.
Base.
W ater.
42.01
48.92
9.07
43.9
47.1
9.0
47.
46.
v-
The atomic constitution, deducible from these proportions*
is one atom of potash, two atoms of carbonic acid, and one
i atom of water.
The bi-carbonate of potash differs from the sub-carbon¬
ate in the following particulars.
1. In the greater mildness of its taste. Though still alka¬
line, yet it may be applied to the tongue, or taken into the
i stomach, without exciting any of that burning sensation,
’ which is occasioned by the sub-carbonate.
2. It is unchanged by exposure to the atmosphere.
3. It assumes the shape of regular crystals. The form of
1’ these crystals is a four-sided prism, with dihedral triangular
■ summits, the facets of which correspond with the solid angles
; of the prism.
4. It requires, for solution, four times it weight of water at
: 60°; and, while dissolving, absorbs caloric. Boiling water
; dissolves five-sixths of its weight; but, during this solution,
! the salt is partly decomposed, as is manifested by the escape
; of carbonic acid gas. The quantity thus separated amounts,
according to Berthollet, to about TV th the weight of the salt.
5. By calcination in a low red heat, the portion of carbonic
! acid, w'hich imparts to this salt its characteristic properties,
i and water, are expelled, and the salt returns to the state of a
sub-carbonate.
(k) Bi-carbonate of potash, in all its forms, is decomposed
I by the stronger acids ; as the sulphuric, nitric, and muriatic,
> which unite with the alkali, and set the gas at liberty.
This may be shown by pouring, on the carbonate contained
i in a gas bottle, any of the acids, and collecting the gas by »
proper apparatus.
\
304*
CARBONATE OF SODA.
CHAP. XI.
Art. 2. — Carbonate of Soda.
There are two distinct compounds of carbonic acid and I
soda, the one containing precisely half as much carbonic acid
as the other.
The first, or sub-carbonate , is obtained by carefully re-crys-
tallizing the soda of commerce. The primitive crystal of this s :
salt is an octohedron, with a rhombic base of 60° and 120°, ,
the planes of which meet, at the summit, at 104°, and, at the
base, at 76°. This crystal varies by becoming cuneiform, and
also by the replacement of the solid angle of the summits by
planes parallel to the base, affording the decahedral variety,
which is most common. These crystals have the following
properties.
1. When heated to 150° Fahrenheit, they fuse; boil vio¬
lently, if the heat be raised ; and leave a dry white powder.
What escapes is water only ; and it forms, according to Be-
rard, 62.69 per cent, of the weight of the salt; to Kirwan, 64 ;
Dalton, 63 ; andD’Arcet, 63.6. The crystals, also, lose their
water by exposure to the atmosphere, or effloresce ,
2. If the fused salt be kept boiling in a retort, Mr. Dalton
finds that it deposits a hard, small-grained salt, which contains
only 46 per cent, of water ; the clear liquid has the specific
gravity of 1.35 ; and, on cooling, concretes into a fragile icy
mass. The first compound, Mr. Dalton estimates to consist
of 1 atom of carbonate and 10 of water ; the second of 1 atom
of salt and 5 of water; and the third of 1 atom of salt and 15
of water.
3. Water at 60° takes up half its weight of the sub-carbon¬
ate ; and boiling water dissolves rather more than its own
weight. The strongest solution, that can be preserved at the
temperature of the atmosphere, has the specific gravity 1.26;
but even this is liable to partial crystallization.
4. If 100 grains of the salt be slowly added to a quantity of
diluted sulphuric acid, more than sufficient for neutralization,
and of known weight, the loss of weight will show the quantity
of carbonic acid contained in 100 grains. From experiments
of this kind, joined w ith others on its loss by fusion, Berard
deduces its composition to be
5
: SECT* IV, CARBONATE OF AMMONIA. 305
Acid . . . . 13.98 .... 100 .... 60
Base .... 23.33 .... 166 . . . ,100
Water . . 62.69
100.
Independently of the water of crystallization, its composition
I has been differently stated, viz. 100 grains contain
Acid. Base.
According to Berard ...... 37.50 . . 62.50
— — — — Dulong ...... 40.09 . . 59.91
— — ■ ■■ ■— Dalton ...... 40.40 . . 59.60
— Klaproth . . . . . 42. . . 58.
______ Kirwan ...... 40.10 . * 59.90
Its atomic constitution is supposed by Mr. Dalton to be one
i atom of soda with one atom of carbonic acid.
When a solution of the sub-carbonate of soda is saturated,
i by passing through it a stream of carbonic acid gas, or when
' a solution of 100 parts of the salt are heated with one of 14
j parts of sub-carbonate of ammonia, we obtain by evaporation
a an indistinctly crystallized salt, which is the bi-carbonate of
, soda . The taste of this salt is much milder than that of the
i sub-carbonate; and it requires a much larger quantity of
ij water for solution. To bring soda to this state of saturation,
100 parts of the alkali require 125.33 of carbonic acid. The
bi-carbonate is, therefore, composed, in 100 parts,
Acid. Base. Water,
According to Berard, of 49.95 . . . .2 9.85 . . . .20.20
- — - - Rose ••..49. ....37. ....14.
And as the acid in this salt is, as nearly as possible, double
that of the sub-carbonate, it must be constituted of two atoms
of acid and one atom of soda. By exposure to a red heat, the
whole of its water, and half its carbonic acid, are expelled,
and it is converted into the dry sub- carbonate.
Art. 3. — Sub-carbonate and Bi-carbonate of Ammonia .
Ammonia, in its pure state, exists in the form of a gas, per¬
manent over mercury only : and carbonic acid has, also, the
form of an aerial fluid* But when these two gases are mixed
VOL. i.
X
306
CARBONATES.
CHAP. XTv
together over mercury in proper proportions (viz. one mea¬
sure of carbonic acid to two or three of alkaline gas), they both
quit the state of gas, and are entirely condensed into a white
solid body. The compound thus formed, it appears from the
recent experiments of Gay Lussac, is the sub-carbonate of
ammonia ; for the two gases, he finds, cannot by simple mix¬
ture, be made to unite in the proportions necessary to neu¬
tralize each other. To effect this, it is necessary to expose a
solution of sub-carbonate of ammonia in water to carbonic acid
gas, in which case the affinity of the water concurs in over¬
coming the elasticity of the acid gas.
(a) Those persons who are not possessed of a mercurial trough
may compose the sub-carbonate of ammonia in the following
manner : — Provide a globular receiver, having two open necks
opposite each other. Into one of these introduce the neck of
a retort, containing carbonate of lime and dilute sulphuric
acid, from which a constant stream of carbonic acid will issue.
The inner surface of the globe will remain perfectly unclouded*
Into the opposite opening, let the mouth of a retort be intro-
dued, containing the materials for ammoniacal gas. (Chap, vih
sect. 2.) The inner surface of the globe will now be covered
with a dense crust of carbonate of ammonia.
The sub-carbonate of ammonia may also be formed, by
passing, into ajar three fourths filled with carbonic acid over
mercury, a solution of pure ammonia, which will instantly
effect an absorption of the gas. The ordinary mode of pro¬
ducing it for useful purposes will be described hereafter.
(i b ) Sub-carbonate of ammonia retains, in a considerable de¬
gree, the pungent smell of the pure volatile alkali. It is, also,
unlike the other sub-carbonates, volatilized by a very moderate
heat, and evaporates without entering previously into a liquid
state. The vapour that arises may be again condensed in a
solid state ; affording an example of sublimation. This may
be shown, by applying heat to the sub-carbonate of ammonia
in a retort, to which a receiver is adapted. The sub-carbonate
will rise, and be condensed in the receiver in the form of a
white crust.
(c) This sub-carbonate does not attract moisture from the
air, but, on the contrary, loses weight.
(d) Sub-carbonate of ammonia, like those of potash and
SECT. IV.
CARBONATE OF AMMONIA.
307
soda, converts vegetable blue colours to green, as the pure al¬
kalies do.
(e) It requires for solution rather more than twice its weight
of cold water, or an equal weight of boiling water. At the
latter temperature, however, it is partly decomposed, and a
violent effervescence ensues.
(f) In composition it varies considerably, according to the
temperature in which it has been formed. Thus, sub-car¬
bonate of ammonia, which has been produced in a temperature
of 300° Fahrenheit, contains 50 per cent, of alkali; while car¬
bonate formed at 60° contains only 20 per cent. By Gay
Lussac*, the sub-carbonate of ammonia is stated to consist of
Ammonia . . .
. 43.98
.... 100 .
. . . 78.57
Carbonic acid
56.02
_ 127.5
«
O
o
9
100.
227.5
178.57
Dr. Ure has lately shown that the most compact and recent
sub-carbonate of ammonia contains water, which becomes ap¬
parent when it is distilled in mixture with dry pulverized quick¬
lime f. This water, he apprehends, constitutes an essential
part of the alkaline base, which, in this view of it, is a hydrate
of ammonia : and the same view may be extended to the other
ammoniacal salts. The proportions of the sub-carbonate, de¬
duced by him from a variety of experiments, are
Ammonia . . 30.5
Carbonic acid .... 54.5
Water . 15.
100.
Or we may consider the sub-carbonate as consisting of 54.5
: acid and 45.5 hydrate of ammonia. By exposure to the air,
! the proportions of its elements are constantly changing, and
i its power of saturating acids decreased.
( a ) It is decomposed by pure potash and pure soda; and
i by the sub-carbonates of those alkalies, which attract its car-
! bonic acid, and expel the alkali. Hence it has been recom-
i mended, by Berthollet, to employ this salt for the full satura¬
tion of potash with carbonic acid, which may be accomplished
! by the following process.
* Memoirs d’Arcueil, ii. 214. t Thomson’s Annals, x. 20ti
x 2
308
CARBONATES.
CHAP. XI.
To a filtered solution of four pounds of pearlash in four
quarts of water, add one pound of carbonate of ammonia, re¬
duced to powder; and stir the mixture at intervals, till the
carbonate of ammonia is entirely dissolved. Filter the liquor,
and put it into a retort, which may be set in a sandbath, and
be connected with a receiver. A very gentle heat is to be ap¬
plied ; so as to distil off about half a pint of the liquor, which
will consist of a solution of carbonate of ammonia in water.
The liquor in the retort may either be allowed to cool in it,
or be transferred into a flat evaporating dish of Wedgwood’s
ware. When cold, crystals of the bi-carbonate of potash will
probably be formed ; otherwise another portion must be dis¬
tilled off, and this must be repeated till the crystals appear ;
separate the first crystals that are formed ; and, on repeating
the distillation and cooling, fresh sets will appear in succes¬
sion. A considerable portion of the solution, however, will
refuse to crystallize. This may be boiled to dryness, and ap¬
plied to the purposes of sub-carbonate of potash. The crys¬
tals of carbonate of potash may be washed with a small quan¬
tity of cold water and dried on blotting paper ; or, if they are
required of great purity, they may be dissolved in cold water,
and re-crystallized, using the gentlest heat possible in evapo¬
rating the solution.
The NEUTRAL CARBONATE Ol’ BI-CARBONATE OF AMMONIA
was formed by Berthollet, by impregnating a solution of sub¬
carbonate with carbonic acid gas. According to his experi¬
ments, it is composed of
Ammonia ........ 28.19 . . . .100 .... 39.2
Carbonic acid .... 71.81 . . . .255 _ 100.
100. 355 139.2
F rom the known specific gravity of those two bodies, Gay
Lussac has calculated that the neutral carbonate consists of
exactly equal quantities by measure of the two gases, while the
sub carbonate is composed of two volumes of alkaline gas to
one of carbonic acid gas.
The bi-carbonate of ammonia may also be formed by ex¬
posing powdered sub-carbonate with a larger and frequently
SECT. IV.
CARBONATE OF BARYTES,
309
renewed surface to the air, till it entirely loses its smell In
I this state it is composed, according to Dr. Ure, of
Carbonic acid ......... 5 1.5
Ammonia ............ 22.8
Water . .............. 22.75 *
The sub-carbonate, by this treatment, has its saturating
< power so much diminished, that 100 grains no longer neu-
! tralize 88 of concentrated sulphuric acid, but only 66. It
i may be doubted, however, whether, when thus obtained, it
? is not a mixture of sub-carbonate and bi-carbonate, since the
\ acid and alkali are not in the proportions to each other, which
are given in the analysis of Berthollet.
mm 10^11 1 1
Art, 4.= — Carbonate of Barytes .
I. Pure barytes has a very powerful affinity for carbonic
. acid.
1. Let a solution of pure barytes be exposed to the atmo¬
sphere. It will soon be covered with a thin white pellicle ;
i which, when broken, will fall to the bottom of the vessel, and
( be succeeded by another. This may be continued, till the
! whole of the barytes is separated. The effect arises from the
absorption of carbonic acid, which is always diffused through
( the atmosphere, and which forms with barytes a substance,
i viz. carbonate of barytes, much less soluble than the pure
; earth.
2. Blow the air from the lungs, by means of a quill, a to-
: bacco- pipe, or glass tube, through a solution of barytes. The
solution will immediately become milky, for the same reason
> as before.
3. With a solution of pure barytes, mingle a little water,
impregnated with carbonic acid. An immediate precipitation
of carbonate of barytes will ensue.
4. Barytes has so strong an affinity for carbonic acid, as
even to take it from other bodies. To a solution of a small
* Thomson’s Annals, x. 207. There appears to be some error, since the
numbers do not make up 100.
310
CARBONATES.
CHAP. XI.
portion of carbonate of potash, of soda, or of ammonia, add
the solution of barytes. The barytes will separate the car¬
bonic acid from the alkali, and will fall down in the state of a
carbonate. By adding a sufficient quantity of a solution of
barytes in hot water, the whole of the carbonic acid may thus
be taken from a carbonated alkali ; and the alkali will remain
perfectly pure.
II. — 1. Carbonate of barytes is nearly insoluble in water,
which, at 60°, does not take up more than part, or,
when boiling, about Water impregnated with carbonic
acid dissolves a considerably larger proportion.
2. Carbonate of barytes is perfectly tasteless, and does not
alter vegetable blue colours. It acts as a violent poison.
3. The combination of carbonic acid with barytes may
either be formed artificially, as in the manner already de¬
scribed, and by other processes, to be detailed in the sequel,
in which case it is termed, the artificial carbonate : or it may
be procured, ready formed, from the earth, and is then called
the native carbonate . It is not, however, a very common pro¬
duction of nature. The largest quantity, hitherto discovered,
is in a mine, now no longer -worked, at Anglezark, near Chor-
ley, in Lancashire.
4. The native and artificial carbonates differ in the propor¬
tion of their components. The former contains, in 100 parts,
20 acid and 80 barytes. The artificial, according to Pelletier,
consists of 22 acid, 62 earth, and 16 water; but in this state¬
ment, there is probably an error, since the proportions between
the acid and earth differ considerably from those which have
been determined by other chemists. Strictly speaking, both
the native and artificial compounds are sub-carbonates ; but as
we are unacquainted with any other compound of barytes and
carbonic acid, they may be allowed to retain the accustomed
name of caibonate. The latest analyses of this compound by
Mr. Aikin, Mr. James Thomson *, and others, fix its com¬
position as follows :
Carb. acid . Barytes .
From Mr, Aikin’s experiments . 21.67 _ 78.33
. . . Thomson's . 21.75 _ 78.25
* Nicholson’s Journal, xxii. xxiii.
! «ECT„ IV. CARBONATE OF STRONTITES. 311
Curb. acid.
Barytes ,
From Mr. Klaproth and Rose’s .. . .
.. 22.00 .
. . . 78.00
— — — — - Bucholz’s ............
. . 21.00 .
. . . 79.00
— — — Berzelius’s
. . 21.60 .
. . . 78.40
. - Dr. Wollaston (from theory) 22.09 .
, . . 77.91
When 100 grains of the carbonate are dissolved in nitric
2 acid, and precipitated by a sulphate, they afford, according
i to Berzelius, 118.6 or 119 grains of sulphate of barytes.
5. Carbonate of barytes is decomposed by an intense heat;
i its carbonic acid being expelled; and the barytes remaining
j pure. The artificial carbonate is most readily decomposed ;
! but the native one is generally employed for obtaining pure
! barytes, because it may be had in considerable quantity. The
{ process, which I have found to answer best, is nearly that of
. Pelletier. Let the native carbonate be powdered, and passed
I through a fine sieve. Work it up with about an equal bulk
i of wTheaten flour into a ball, adding a sufficient quantity of
water. Fill a crucible of proper size, about one third its
1 height, with powdered charcoal ; place the ball on this ; and
surround and cover it with the same powder, so as to prevent
i its coming into contact with the sides of the crucible. Lute
i on a cover ; and expose it, for two hours, to the most violent
1 heat that can be raised in a wind furnace. Let the ball be
; removed when cold. On the addition of water, it will evolve
j great heat, as already described (chap, viii.), and the barytes
will be dissolved. The filtered solution, on cooling, will shoot
; into beautiful crystals.
6. Carbonate of barytes is decomposed by the sulphuric,
; nitric, muriatic, and various other acids, which detach the
' carbonic acid, and combine with the earth.
Art. 5.— Carbonate of Strontites.
The relation of strontites to carbonic acid resembles, very
1 closely, that of barytes ; and all the experiments, directed to
be made with the solution of the latter earth, may be repeated
with that of strontites, which will exhibit similar appearances*
* 78 Ann. de China. 29.
312
CARBONATES.
CHAP. XI
The carbonate of strontites requires for solution 1536 parts
of boiling water. It is found native, but containing a little
carbonate of lime, at Strontian in Argyleshire ; and may, also,
be prepared by artificial processes, which will be afterwards
described. From this carbonate pure strontites may be pre«
pared, by treating it in the same manner as was directed for
the calcination of carbonate of barytes.
The artificial carbonate, according to Stromeyer *, does not
essentially contain any water. It consists of
Strontites . . . 70.313 or 100
Carbonic acid ........ 29.687 . . 42.22
100.
Art. 6.~ Carbonate of Lime .
1. Lime has a strong attraction for carbonic acid, but not
*
when perfectly dry.
(a) If a piece of dry quicklime be passed into a jar of car¬
bonic acid gas over mercury, no absorption ensues. But in¬
vert a bottle, filled with carbonic acid gas, over a mixture of
lime and water of the consistence of cream, and a rapid ab¬
sorption will be observed, especially if the bottle be agitated.
( b ) Let a jar or bottle, filled with carbonic acid, be brought
over a vessel of lime water. On agitating the vessel, a rapid
diminution will ensue, and the lime water will become milky.
(c) Leave a shallow vessel of lime water exposed to the air.
A white crust will form on the surface, and this, if broken,
will fall to the bottom, and be succeeded by another. This is
owing to the absorption of carbonic acid gas from the air by
the lime, which is thus rendered insoluble in water.
(i d ) Lime, when exposed to the atmosphere, first acquires
moisture, and then carbonic acid ; and, in a sufficient space of
time, all the characters distinguishing it as lime disappear.
(e) Lime has an extremely strong affinity for carbonic acid,
which enables it to take this acid from other substances. Thus
carbonates of alkalies are decomposed by lime. Slake a given
* Ann de Chim, et Phys. iii. 396.
SECT. IV. CARBONATE OF LIME. 313
j quantity of lime into a paste with water, and add half its
' weight of carbonate of potash or soda. Boil the mixture, for
half an hour, in an iron kettle, and separate the liquid part
by filtration or by subsidence. The carbonic acid combines
> with the lime, and the alkali is obtained in a state of solution
perfectly free from carbonic acid. This is the ordinary mode
of depriving the alkalies of carbonic acid.
(f) Lime, when saturated with carbonic acid, must ncces-
i sarily form bi-carbonate of lime. We are unacquainted, how-
• ever, with this salt, and it is chiefly by a process of reasoning
I that Berthollet has shown it must consist of 100 parts of lime
united to 150.6 carbonic acid; whereas in the sub-carbonate
100 parts of lime are combined with only half that quantity *.
Of this, common chalk, or Carrara marble, may be taken as a
fair sample; and in all sub-carbonates of this earth, we find
the characters of insipidity and insolubility in wTater„ Cal¬
careous spar, marble, stalactites, lime-stone, and chalk, are
all varieties of sub-carbonate of lime. It contains per cent.
Acid. Base.
According to Wollaston . 43.7 .... 56.3
— — - - Berzelius . 43.6 .... 56.4
— - — - — * Dr. Ure . . 43.52 _ 56.48
It appears to be constituted of an atom of lime united with an
atom of carbonic acid.
(g) Carbonate of lime is decomposed by a strong heat. If
distilled in an earthen retort, carbonic acid gas is obtained,
and lime remains in the retort in a pure or caustic state. By
this process it loses about 45 per cent.
The very curious and important experiments of Sir James
Hall have proved, that when the escape of the carbonic acid
is prevented by strong pressure, carbonate of lime is fusible in
a heat of about 22° of Wedgwood’s pyrometer f. And Mr.
Bucholz has lately fused this substance, by the sudden appli¬
cation of a violent heat, without additional compression f.
( h ) Carbonate of lime is decomposed by the stronger acids.
Put some chalk into a gas bottle, and pour on it diluted sul-
* Memoires d’Arcueil, ii. 478.
J Nicholson’s Journal, xvii. 229.
t Nicholson’s Journal, xiii. xiv„
314
CARBONATES.
CHAP. XI.
phuric acid. The sulphuric acid will unite with the lime, and
the carbonic acid will be set at liberty. One hundred grains
of carbonate of lime, according to PfafF, are saturated by 88
grains of sulphuric acid of the specific gravity 1854; and give
129.4 of sulphate of lime. These numbers, however, are not
consistent with the known composition of carbonate and sul¬
phate of lime, which requires that 100 grains of the carbonate
should be saturated by 97.5 of oil of vitriol of the specific
gravity 1850, and that there should result 136 of calcined
sulphate of lime.
By a comparison of this experiment with the preceding
one (g), we may learn the proportion of carbonic acid and
water contained in any carbonate of lime. Let 100 grains of
the carbonate be put into a Florence cask, with an ounce or
two of water ; place this in the scale of a balance ; and in the
same scale, but in a separate bottle, about half an ounce of
muriatic acid. Add the muriatic acid to the carbonate as
long as any effervescence is produced, and then blow out the
disengaged carbonic acid, which remains in the flask, by a
pair of bellows. Ascertain, by adding weights to the opposite
scale, how much has been lost ; suppose it to be forty grains ;
this shows the quantity of carbonic acid disengaged. Calcine
another 100 grains in a covered crucible. It will lose still
more of its weight; because, besides its carbonic acid, all the
water is expelled which it may contain. Let this loss be stated
at 45 grains; the former loss deducted from this (45—40), or
5 grains, shows the quantity of water in 100 of the carbonate.
(i) Carbonate of lime, though scarcely dissolved by pure
water, is soluble in water saturated with carbonic acid. The
most striking method of showing this is the following : Add
to a jar, about one fourth filled with lime w7ater, a very small
quantity of water saturated with carbonic acid. An imme¬
diate milkiness will ensue, because the carbonic acid forms
with the lime an insoluble carbonate. Add gradually more of
the water, impregnated with carbonic acid, shaking the jar as
these additions are made. At last the precipitate is re-dis¬
solved. Hence it appears that lime, with a certain proportion
of carbonic acid, is insoluble, and, wTith a still larger, again
becomes soluble in water.
2
SECT. IV. CARBONATE OF MAGNESIA. 315
(k) The carbonate of lime, dissolved by an excess of car-
! bonic acid (i), is again separated, when this excess is driven
i off. Thus boiling, which expels the superabundant acid, pre-
> cipitates the carbonate. Caustic, or pure alkalies, also pro¬
duce a similar effect.
Art. 7. — Carbonate of Magnesia .
I. Pure magnesia does not attract carbonic acid with nearly
the same intensity as lime. Hence magnesia may be exposed
to the air, without any important change in its properties, or
much increase of weight, unless the exposure be long con¬
tinued, when it first becomes a hydrate by absorbing water,
and then attracts carbonic acid from the atmosphere. The
carbonate of magnesia, used in medicine, and for experimental
purposes, is prepared by a process to be described in the
sequel. In this state, however, it is not entirely saturated with
carbonic acid, and is rather a sub-carbonate. Its composi¬
tion Bucholz states to vary, as it is prepared with or without
heat. If the former, it contains per cent. 42 base, 35 acid,
23 water; if prepared from cold solutions of sub- carbonate of
soda and sulphate of magnesia, it consists of 33 base, 32 acid,
and 35 water. Mr. Dalton makes it to be composed of 43
base, 40 acid, and 17 water, which numbers indicate that it
is constituted of one atom of acid, one of earth, and one of
water. Berzelius is of opinion that it is a compound of three
atoms of carbonate of magnesia with one atom of the hydrate
of the same earth *.
II. The saturated carbonate (as it has generally been con¬
sidered) may be obtained, by passing streams of carbonic acid
gas through water, in which the sub-carbonate is kept me¬
chanically suspended. The solution yields, when evaporated,
small crystals, which are transparent hexagonal prisms, ter¬
minated by hexagonal planes. These crystals have no taste,
and are soluble in 48 parts of cold water ; whereas the sub¬
carbonate requires at least ten times that quantity. The crys¬
tallized carbonate contains per cent. 30 acid, 30 earth, and 40
* Thomson's Annals, xii. 30.
316
CARBONOUS OXIDE.
CHAP. XI.-
water, so that it is in reality constituted like the common car¬
bonate, but with three atoms of water instead of one.
III. The carbonate of magnesia is decomposed by the same
agents as the carbonate of lime. It yields its carbonic acid,
however, in a much more moderate heat.
IV. Lime has a stronger affinity than magnesia for carbonic
acid. Hence, if lime water be digested with carbonate of
magnesia, the lime is precipitated in the state of an insoluble
carbonate.
Art. 8.— Carbonate of Glucine.
Glucine appears to have a considerable affinity for carbonic
acid; for, when precipitated from acids by pure alkalies, and
dried in the air, it becomes effervescent. The carbonate of
glucine is white, insipid, insoluble, and very light. It con¬
tains about one fourth its weight of carbonic acid, which it
loses by exposure to a low red heat.
The carbonate of silex does not exist, and those of zircon,
alumine, and yttria, have no peculiarly interesting properties.
SECTION V,
Gaseous Oxide of Carbon , or Carbonous Oxide.
This combination of carbon with oxygen contains a less
proportion of oxygen than is found in carbonic acid. Its dis¬
covery was announced in Nicholson’s Journal, for April, 1801,
by Mr. Cruickshank, and in the 38th volume of the Armales
de Chimie , by Clement and Desormes, whose experiments are
continued in the 39th volume of the same work, p. 26. The
Dutch chemists, however, in volume 43, object to its being
considered as a distinct gas, and regard it merely as a carbu¬
ret of hydrogen. But their objections do not appear sufficient
to prevent the acknowledgment of the gaseous oxide as a new
and peculiar species.
It may be procured by any of the following processes :
1. By the distillation of the white oxide of zinc with one
CARBONOCS OXIDE.
317
i SECT. V.
i eighth of its weight of charcoal, in an earthen or glass retort;
I from the scales which fly from iron in forging, mixed with a
! similar proportion of charcoal ; from the oxides of lead, man-
I ganese, or, indeed, of almost every imperfect metal, when
heated in contact with powdered charcoal. It may also be
obtained from the substance which remains after preparing
; acetic acid from acetate of copper.
2. From well dried carbonate of barytes or of lime (com¬
mon chalk), distilled with about one fifth of charcoal ; or with
rather a larger proportion of dry iron or zinc filings, which
afford it quite free from hydrogen.
3. By transmitting carbonic acid gas over charcoal ignited
in a porcelain tube. The acid gas combines with an additional
dose of charcoal ; loses its acid properties ; and is converted
into the carbonous oxide. An ingenious apparatus, contrived
by M. Baruel, and extremely useful for this and similar pur¬
poses, is described and represented by a plate, in the 1 1th
volume of Nicholson’s Journal.
The last product of the distillation is the purest, but still
contains carbonic acid, which must be separated by washing
the gas with lime liquor.
Its properties are as follow :
(a) It has an offensive smell..
(5) It is lighter than common air, in the proportion of 966
to 1000. One hundred cubical inches wreigh 30 grains, the
temperature being 55° Fahrenheit, and pressure 29.5 (Cruick-
shank); or at temperature 60°, and barometer 30, 100 cubic
inches weigh 30.19 grains. Its specific gravity from calcula¬
tion, according to Gay Lussac, should be .96782.
(c) It is inflammable, and, when set fire to, as it issues from
the orifice of a small pipe, burns with a blue flame. When
mixed with common air, it does not explode like other inflam¬
mable gases, unless in very few proportions but burns
silently with a lambent blue flame. A mixture of two mea¬
sures with one measure of common air may, however, be ex¬
ploded by a lighted taper, or even by red-hot iron or charcoal,
(d) When a stream of this gas is burnt, in the manner de-
* Dalton’s System, p. 373.
318
CARBONOUS OXIDE.
CHAP. XI.
scribed in speaking of hydrogen gas, no water is condensed
on the inner surface of the glass globe, a proof that the
gaseous oxide contains no hydrogen. Berthollet, indeed, still
contends, in opposition to most chemists (and among others
to Gay Lussac), that hydrogen is one of the elements of this
gaS*
(e) It is sparingly soluble in water ; is not absorbed by liquid
caustic alkalies ; nor does it precipitate lime water.
(f) It is extremely noxious to animals ; and fatal to them
if confined in it. When respired for a few minutes, it pro¬
duces giddiness and fainting *.
(g) When 100 measures of carbonous oxide are fired over
mercury in a detonating tube, with 45 of oxygen gas, the
total 145 are diminished to 90, which, if the gases employed
be pure, consist entirely of carbonic acid. Proportions, dif¬
fering a little from these, have been stated by Berthollet, viz.
that 100 measures of carbonous oxide are saturated by 50
measures of oxygen, and give 100 of carbonic acid ; and these
last proportions are coincident, also, both with the theory and
experience of Gay Lussac.
(h) It is not expanded by electric shocks, nor does it appear
to undergo any change by electrization.
(i) When the carbonous oxide, mingled with an equal
bulk of hydrogen gas, is passed through an ignited tube, the
tube becomes lined with charcoal. In this temperature, the
hydrogen attracts oxygen more strongly than it is retained by
the charcoal, and forms water. It was found, also, by Gay
Lussac to be decomposed by the action of potassium, which
combines with the oxygen and precipitates charcoal.
According to Mr. Cruickshank, it contains per cent, about
70 oxygen, and 30 carbon by weight ; or the former is to the
latter as 21 to 8.6, or as 21 to 9. Gay Lussac, however,
makes it to consist of 43 charcoal and 57 oxygen ; Berzelius
of 44.28 charcoal and 55.72 oxygen, proportions which agree,
within a small fraction, with those of Clement and Desormes.
It contains, therefore, just half the oxygen that exists in car¬
bonic acid ; and it is constituted of one atom of charcoal and
i
* See Phil. Mag. xliii. 367.
SECT. VI. CARBURETED HYDROGEN GAS. 31 $
one atom of oxygen, and weighs, according to Mr. Dalton,
7 + 5.4 = 12.4, or, by the corrected numbers, 7 .5 + 5.8 = 13.8.
SECTION VI.
Combination of Carbon with Hydrogen , forming Carbureted
Hydrogen Gas , or Hydro- Carburet,
I. Of this combination there appear, on first view, to be
f several distinct varieties, consisting of carbon and hydrogen,
united in various proportions, and obtained by different pro-
: cesses.
1. When the vapour of water is brought into contact with
' red-hot charcoal (by means of an apparatus similar to that
represented, fig. 40), two different products are obtained.
The oxygen of the water, uniting with the carbon, consti¬
tutes carbonous oxide and carbonic acid ; and the hydrogen
of the water dissolving, at the moment of its liberation, a
: portion of charcoal composes carbureted hydrogen gas The
5 carbonic acid may be separated from the hydro-carburet, by
i agitating the gas, which has been produced, in contact with
; lime and water, mixed together, so as to be of the consistence
: of cream. '
2. By stirring, with a stick, the mud that is deposited at
i the bottom of ditches or stagnant pools, bubbles of gas ascend
| to the surface, and may be collected in an inverted bottle of
• water, to the mouth of which a funnel, also inverted, is fixed.
3. By submitting coal to distillation, in an iron or coated
| glass retort, a large quantity of gas, besides a portion of tar,
is produced. The latter may be received in an intermediate
i vessel; and the gas must be well washed with lime liquor.
. The first product only is to be reserved as a specimen of coal
j gas ; for, as the distillation proceeds, its density becomes gra-
i dually less ; till, at length, the gas, which is produced at the
i close of the operation, is only about half as heavy as that
* In Nicholson’s Journal, xi. 68, I have stated my reasons for believing
1 that this gas is not pure hydro-carburet.
820
CARBURETED HYDROGEN GAS.
CHAP. XI.
evolved at first. The quantity of gas, also, which is produced
from a given weight of coal, is so variable from different kinds
of this mineral, and is so much influenced by the degree of
heat employed in its production, that it is scarcely possible to
state any general average. From 120 pounds avoirdupois of
the sort of coal called Wigan Carmel , about 340 cubic feet of
gas may be obtained, of which half a cubic foot per hour is
equal to a mould candle of six to the pound, burning during
the same space of time.
4. Let a porcelain tube, coated with clay, be fixed hori¬
zontally in a furnace, in the manner represented, fig. 40. To
one end let a retort be luted, containing an ounce or two of
ether or alcohol ; and, to the other, a bent tube, which ter¬
minates under the shelf of the pneumatic trough. A gas will
be disengaged, on igniting the tube, and transmitting, through
it, the alcohol or ether in vapour, which, when w'ashed with
lime-liquor, is the carbureted hydrogen.
5. A fifth mode of obtaining hydro-carburet, discovered
by the Dutch chemists *, consists in distilling, in a glass re¬
tort, with a gentle heat, three measures of concentrated sul¬
phuric acid, and one measure of alcohol. The mixture
assumes a black colour and thick consistence; and bubbles of
gas are disengaged, which may be collected over water. For
reasons which will be stated when we come to speak of chlo¬
rine, this gas has been named the olefiant gas.
IL- — 1. These different gases vary considerably, in density
or specific gravity. Atmospheric air being 1000, the specific
gravity of gas from moistened charcoal is 480 ; from ether or
alcohol 520 ; from pit-coal between 300 and 780, according to
the period of the distillation, at which it is collected, the
early products being always the heaviest. Gas from stagnant
water , according to Mr. Dalton, is of the specific gravity 600,
and hence 100 cubic inches must weigh 18.3 ; but Dr. Thom¬
son fixes its specific gravity at 555, which would give only
16.93 grains for 100 cubic inches. The specific gravity of
olefiant gas is stated by the Dutch chemists, its discoverers,
at 909, by Dalton and Henry at 967 or 950, by Saussure at
* Nicholson’s Journal, 4to. i. 41.
SECT. vr.
HYDKO-CARBURET GASES.
321
978.4, by Dr. Thomson at 974 ; and by Gay Lussac, from
calculation, at 978. From the last number, the weight of
100 cubic inches at 60° Fahrenheit, and 30 inches barometer,
I may be deduced to be 29.72 grains.
2. These gases differ as to the quantity, which water is
: capable of absorbing ; for of the olefiant gas it takes up xth of
' its bulk ; of gas from stagnant water ; and of the others
still less.
3. The varieties of carbureted hydrogen gas all agree in
: being inflammable ; but they possess this property in \Tarious
degrees, as is evinced by the variable brightness of the flame,
’ which they yield when set on fire ; and by the different tem¬
peratures at which they begin to burn. Light carbureted hy-
! drogen, or fire-damp, requires a much stronger heat to excite
i its combustion than olefiant gas. They may be inflamed as
! they proceed from the orifice of a small pipe, or from between
two concentric cylinders of sheet-iron or copper, placed at the
I distance of a small fraction of an inch from each other. On
i this principle, an Argand’s lamp may be constructed, for
! burning the gases, which will issue from that space, com-
i monly occupied by the wick.
When burned in either of these modes, there is a manifest
> gradation in the density and brightness of the flame, corres-
{ ponding to the quantity of solid charcoal which is first depo-
sited, and afterwards burned. The gas from charcoal burns
i with a faint blue light, not suited to the purpose of illumination;
, that from ether or alcohol with more brilliancy; but still short
i of that with which the coal gas burns, when recently prc-
| pared ; and the first product of gas from a given quantity of
j coal, affords at least twice as much light, as an equal volume
t of the last portions. The olefiant gas surpasses them all, in
the quantity of light evolved by its combustion. It continues
t to bum in air, the density of which is diminished 10 or 11
times, whereas gas from stagnant water affords a flame, which
i is extinguished in air rarefied more than one fourth. Another
i important distinction between the several kinds of carbureted
i hydrogen is derived from the results of mixing each of them
* with chlorine, which will be described in the chapter on that
f substance.
VOL. I. Y
322
HYDRO-CARBURET GASES.
CHAP; XE
If these gases be burned in a vessel of oxygen gas over
lime-water, by means of a bladder and bent brass pipe (pi. iv.
fig. 41), two distinct products are obtained, viz . water and
carbonic acid. That water is produced, may be shown by
burning a very small stream of this gas, under a long funnel-
shaped tube open at both ends. The formation of carbonic
acid is evinced, by the copious precipitation of the lime-water
in the foregoing experiment.
The composition of each of the above gases is learned by
firing it, in a detonating tube over mercury, with a known
quantity of oxygen gas ; and observing the nature and quan¬
tity of the products. These products are carbonic acid and
water. The former may be exactly measured ; but the water
is generated in such small quantity, that it can only be com¬
puted. The following table shows the results of a few experi¬
ments of this kind.
Measures of Oxygen Measures of
Kind of Gas. Gas required to satu- Carbonic Acid
rate 100 Measures. produced.
Pure hydrogen gas ........ 50 to 54 . . . —
Gas from charcoal ........ 60 . . 35
— — — coal . . . 190 . 97.5
— — stagnant water . . . 200 . . 100
Olefiant gas , . . . 300 . . . . 200
Now since, for the formation of each measure of carbonic
acid gas, in the foregoing experiments, an equal volume of
oxygen gas is required, we may learn, by deducting the num¬
ber in the third column from the corresponding one in the
second, what proportion of oxygen has been spent in the
saturation of the hydrogen of each variety of hydro-carburetv
Thus, for example, in burning the gas from stagnant water,
100 measures of oxygen have been employed in forming car¬
bonic acid; and the remaining 100 in saturating hydrogen.
But 100 measures of oxygen are sufficient to saturate 200 of
hydrogen gas ; and a quantity of hydrogen must therefore
be contained in 100 measures of gas from stagnant water;
which, expanded to its usual elasticity, would occupy 200
measures.
From these data, it is easy to deduce the composition of
SECT. VI.
HYBROCARBURET GASES.
323
this variety of carbureted hydrogen ; for if its specific gravity
be 0.6,
Crains*
100 cubic inches must weigh ...................... 18,3
The 100 cubic inches of carbonic acid produced"! 0
weigh 47 grains, and contain of charcoal ...... j
Hence the hydrogen, in 100 cubic inches, weighs .... 5.1
Or 104 grains of gas from stagnant water are composed of
Carbon ........ 72
Hydrogen ...... 28
100
These results accord best with the opinion tnat this gas,
which may be called simply carbureted hydrogen , is constituted
of one atom of charcoal and two atoms of hydrogen.
Olefiant gas, pei'-carbureted hydrogen , or bi-carbureted hy¬
drogen, investigated in precisely the same manner, is com¬
posed, in 100 grains,
Carbon. Hydrogen.
According to Dr. Thomson *, of . , . . 85 . . 15
- — — — — — Saussure, jun. of ....... . 86 . . 14
It consists, therefore, according to Mr. Dalton, of one
(atom of carbon and one atom of hydrogen. This would
make the weight of an atom of charcoal 5.66; for 85 is to 15
as 5.66 to 1 ; a result which coincides, as nearly as can be ex¬
pected, with the weight of the atom of charcoal, already de¬
duced from the composition of carbonic acid, vi%. 5.65.
The only distinct and well characterized species of car¬
bureted hydrogen appear to me to be olefiant gas, or per-car -
bureted hydrogen; and the gas from stagnant water, called
simply carbureted hydrogen , to which the epithet light is pre¬
fixed by some chemists, on account of its inferior specific
gravity. Of these, with occasionally a portion of carbonic
oxide, and other inflammable gases, the other varieties ap¬
pear to be mixtures. The coal gas, for example, which is
now so generally used for the purpose of affording light, I
324 HYDRO-CARBURET GASES. CHAP. XI. ,
have shown* to be a mixture of at least five others, the pro¬
portion of which varies at every successive stage ol the distil¬
lation of coal. It has been contended, indeed, by Berthollet,
Murray, and other philosophers, that carbon and hydrogen i
are capable of uniting in a variety of proportions , not only
with each other, but with oxygen. But there seems reason t
to believe, from a careful examination of all the best experi¬
ments on these compounds, that hydrogen and carbon unite
only in two definite proportions , and that these proportions are
no other, than those constituting carbureted and per-carbureted
hydrogen gases, viz. in the former one atom of charcoal to
two atoms of hydrogen, and in the latter an atom of each of
those combustible bodies.
On the Fire Damp of Coal Mines , and the Construction and
Principle of the Safety-Lamp of Sir H. Davy.
The fire-damp of coal mines, by an analysis of it which I
published in 1806, was shown to be identical in composition i
with light carbureted hydrogen f . This conclusion coincides
with the subsequent results of Sir H. Davy, who has enlarged
our knowledge of the chemical history of the fire-damp, by
several important facts J. The most readily explosive mixture
of fire-damp with common air he found to be one measure of
the gas to seven or eight of air. This mixture was not set on
fire by charcoal in a state of active combustion, nor by iron
ignited to a red or even to a white heat, except when in a
state of brilliant combustion; in which respects, the fire-damp
differs from other combustible gases.
It was in attempting to measure the expansion, occasioned
by the combustion of a mixture of fire-damp and air, that Sir
H. Davy discovered a fact, which afterwards led him to the
most novel and important results. An explosive mixture
could not, he ascertained, be kindled in a glass tube so narrow
as a of an inch diameter ; and when two separate reservoirs
of an explosive mixture were connected by a metallic tube,
A of an inch diameter and \\ inch in length, and one of the
* Phil. Trans. 1808.
| Phil. Trans. 1816.
f Nicholson's Journal, xix. 149.
SECT. Vi.
FIRE-DAMP OF COAL MINES.
32 5
portions of gas was set on fire, the explosion did not extend
to the other. Fine wire sieves or wire gauze, interposed
between two separate quantities of an explosive mixture, were
also found to prevent the combustion of one portion from
spreading to the other. A mixture of fire-damp and air in
explosive proportions, was deprived of its power of exploding
by the addition of about y its bulk of carbonic acid or nitrogen
gas.
Reflection on these facts suggested to Sir H. Davy the pos¬
sibility of constructing a lamp *, in which the flame, by being
supplied with only a limited quantity of air, might produce
carbonic acid and nitrogen in such proportion as to destroy
the combustibility of explosive mixtures ; and which might,
also, by the nature of its apertures for giving admittance and
exit to the air, be rendered incapable of spreading combus¬
tion to the surrounding atmosphere, supposing this to be an
inflammable one.
This most desirable object was accomplished by the use of
air-tight lanterns, supplied with air through tubes or canals
of small diameter, or through apertures covered with wire
gauze below the flame, and having a chimney at the upper
part on a similar system, for carrying off the foul air. The
apparatus was afterwards simplified, by covering or surround¬
ing the flame of a lamp or candle with a cylindrical wire
sieve, having at least 625 apertures in a square inch. Within
this cylinder, when the fire damp encompassing it is to the
air as 1 to 12, the flame of the wick is seen surrounded by
the feeble blue flame of the gas. When the proportion is as
1 to 5, 6, or 7, the cylinder is filled with the flame of the
fire-damp; but though the wire gauze becomes red-hot, the
exterior air, even when explosive, is not kindled. The lamp
is therefore safe in the most dangerous atmospheres, and has
been used most extensively in the mines of Whitehaven, New¬
castle, and other places, without the occurrence of a single
failure or accident.
* A full history of the Safety Lamp, and of the chemical researches
connected with it, has lately been published by Sir H. Davy, 8vo. printed
for E. Hunter, 1818.
326 PRINCIPLE OF THE SAFETY-LAMP. CHAP. XI,
The effect of the safety-lamp depends on the cooling agency
of the wire gauze, exerted on the portion of gas burning within
the cylinder. Hence a lamp may be secure where there is no
current of an explosive mixture to occasion its being strongly
heated ; and yet not safe, when the current passes through it
with great rapidity. But any atmosphere, however explosive,
may be rendered harmless, by increasing the cooling surface ;
which may be done, either by diminishing the size of the aper¬
tures, or by increasing their depth, both of which are perfectly
within the power of the manufacture of the wire gauze.
When a small coil of platinum wire is hung above the wick
of the lamp within the wire gauze cylinder, the metal con¬
tinues to glow, long after the lamp is extinguished, and affords
light enough to guide the miner in what would otherwise be
impenetrable darkness. In this case, the combustion of the
fire damp is continued so slowly, and at so low a temperature,
as not to be adequate to that ignition of gaseous matter which
constitutes flame, though it excites a temperature sufficient to
render platinum wire luminous. A similar ignition of platinum
wire, it has lately been found, may be supported for many
hours, by surrounding the flame of a spirit lamp with small
coils of that metal, not exceeding of an inch in diameter.
Twelve coils of this wire, twisted spirally round the tube of a
tobacco-pipe, or round any thing that will render the coils
about of an inch in diameter, are to surround, six the
wick of the lamp, and six to remain elevated above the wick.
The wick should be small, and quite loose in the burner of the
lamp ; and the fibres of the cotton, surrounded by the coil,
should be laid as straight as possible. When the lamp, after
being lighted for a few moments, is blown out, the platinum
wire continues to glow for several hours, as long as there is a
supply of spirit of wine, and to give light enough to read by ;
and sometimes the heat produced is sufficient to re-kindle the
lamp spontaneously *.
Thomson’s Annals, vol. xi.
Z73
! SECT. VI*. CARBURET OR NITROGEN OR CYANOGEN. 32?
SECTION VIE
Carburet of Nitrogen , o?* Cyanogen .
To obtain cyanogen, it is necessary first to prepare a pure
prussiate of mercury, by boiling fine powdered red oxide of
! mercury with twice its weight of prussian blue and a sufficient
quantity of water. The compound is perfectly neutral, and
crystallizes in long four-sided prisms truncated obliquely. It
$ still, however, contains a little iron, which may be separated by
digesting the liquor, before evaporation, with a little more of the
i oxide of mercury, and saturating the excess of this oxide with
a little prussic acid (see -vol. ii.), or even with a little muriatic
: acid. The prussiate of mercury, thus obtained, must be com¬
pletely dried at a temperature below that of boiling water, and
j then exposed to heat in a small retort, or in a tube closed at
one extremity. It first blackens, then liquifies, and the cya¬
nogen comes over in the form of a gas, which may be collected
over mercury. In the retort there remains a charry matter
of the colour of soot, and as light as lamp black *.
1. Cyanogen is a true gas, or permanently elastic fluid. Its
smell is strong and penetrating. It burns with a bluish flame
: mixed with purple. Its specific gravity is to that of common
air as 1.8064 to 1. Hence 100 cubic inches at 60° Fahr*
weigh 55 grains.
2. Water at the temperature of 60° Fahr. absorbs almost
4A times its volume, and pure alcohol 23 times its volume.
3. When 100 measures of cyanogen are detonated, in
a Volta’s eudiometer, with 250 measures of oxygen gas, 200
measures of carbonic acid result; and 100 measures of nitro¬
gen. There remain, also, 50 measures of oxygen gas uncon¬
densed. From these data, it is calculated by Gay Lussac, that
cyanogen is composed of two volumes of the vapour of char-
: coal and one volume of nitrogen, condensed into a single
volume. Its density ought, therefore, to be 1.8011, a number
not very remote from that obtained by experiment.
4. Analysis by more complicated methods afforded the same
* Gay Lussac, Ana, de Chim. vol. xcv, ; or Thomson's Annals, viii. 37.
528
CARBURET OF NITROGEN, OR CYANOGEN. CHAP. XI.
result, evincing that cyanogen yields, by a decomposition
effected by means of oxygen, twice its volume of carbonic acid
and an equal volume of nitrogen. No water whatsoever is
formed during its combustion, if the gas be perfectly free from
prussic acid vapour, a sufficient proof of the absence of hy¬
drogen from its composition.
5. The solutions of pure alkalies and alkaline earths absorb
cyanogen ; and the liquid obtained, when poured into a solu¬
tion of black oxide of iron, affords prussian blue, but not
without the addition of an acid. At the same time, carbonic
acid gas escapes in volume equivalent to the cyanogen absorbed,
and there is a perceptible smell of prussic acid. These changes
will be more evident from the following recapitulation :
1 vol. of
cyanogen
f— 2 vol. char-
coal and 1 vol.
nitrogen .
}
decomposes
1 atom of
water
— 1 vol. oxygen
and 2 vol. hy¬
drogen.
One volume of charcoal, uniting with one volume of oxygen,
forms one volume of carbonic acid ; the remaining volume of
charcoal, uniting with half a volume of nitrogen and half a
volume of hydrogen, composes prussic acid ; and the residuary
half volume of nitrogen and 1-J. volume of hydrogen com¬
pose together one volume of ammonia.
6. It will afterwards be shown, that when to two volumes
of charcoal and one volume of nitrogen, together constituting
cyanogen, one volume of hydrogen is joined, and the whole
condensed into two volumes, we obtain prussic acid. Cyano¬
gen agrees then with chlorine and iodine, in being acidifiable
by union with hydrogen. Hence its compounds with metallic
bases have been called by Gay Lussac cyanures , as those of
chlorine are called chlorures ; but having elsewhere expressed
a preference for the name of chlorides , I shall, from analogy*
give to the compounds of cyanogen the name of cyanides.
329
*•
CHAPTER XII.
SULPHUR.— SULPHURIC ACID.— SULPHATES. — BINARY
COMPOUNDS OF SULPHUR.
IN describing sulphur and its compounds, I shall take them
in the following order :
I. Sulphur in its un combined state.
II. Sulphur united with its full proportion of oxygen, con¬
stituting sulphuric ACID ; and the compounds of this acid
with alkalies and earths, termed sulphates.
III. Sulphur united with a less proportion of oxygen, com¬
posing sulphurous acid ; and the compounds of this acid,
called sulphites. It appears, also, from recent experi¬
ments, that there is a third acid, consituted of sulphur with a
still less proportion of oxygen. This acid is at present known
only in combination. It is called hypo-sulphurous or per-
SULPHUROUS ACID.
IV. The compounds of sulphur with alkalies and earths,
termed sulphurets.
V. The combination of sulphur and hydrogen, named sul-
phuretEd hydrogen ; and the compounds, which it forms
with alkaline and earthy bases, called hydro-sulphurets.
VI. The compound of sulphureted hydrogen with a still
farther quantity of sulphur, composing super-sulphureted
hydrogen ; and its compounds with different bases called
hydrogureted sulphurets, or sometimes sulphureted-
hydro-sulpilurets.
SECTION I.
SULPHUR.
I. The sulphur, wdiich occurs as an article of commerce, is
a mineral production, and is brought to this country chiefly
from Sicily. That which is procured in our own island, is
generally of very inferior quality, and contains a portion of
3
330
SULPHUR.
CHAP. XI r.
the metal, from combination with which it has been separated*
It is met with under two different forms ; of a compact solid,
which has generally the shape of long rolls or sticks; and of
a light powder called flowers of sulphur . In general, the latter
may be considered as most pure ; but the two varieties, it will
presently appear, are readily convertible into each other by
the modified application of heat. Its specific gravity is 1.98
or 1.99.
II. Sulphur is readily fused and volatilized. When heated
to 170° of Fahrenheit, it begins to evaporate, and to produce
a very disagreeable smell ; at 185° or 190° it begins to melt;
and at 220° is completely fluid. If the heat be rapidly in¬
creased, it loses at 350° its fluidity, and becomes firm, and of
a deeper colour. It regains its fluidity, if we reduce the tem¬
perature ; and this may be repeated at pleasure, in close glass
vessels, if the changes of heat be not slow ; otherwise it is
volatilized. It sublimes at 600°.
III. If, after being melted, it be suffered to cool, it con¬
geals in a crystalline form, but so confusedly, that we cannot
define the shape of the crystals, farther than that they are
slender interlaced fibres. If a large mass be kept fluid below,
while it congeals at the surface, the crystallization there is
much more distinct. When sulphur in complete fusion, viz,
at 300°, is poured into water, it become tenacious like wax,
and may be applied (as is done by Mr. Tassie) to take im¬
pressions from engraved stones, &c. These impressions are
quite hard, when the sulphur has become cold. It is then of
a red colour, and of the specific gravity 2.325.
IV. At the temperature of about 290° Fahrenheit, sulphur
is converted into vapour; and if this operation be conducted
in close vessels, the volatilized 'sulphur is again collected in a
solid form. What remains has been called sulphur vivum .
This affords an example of the process of sublimation , which
differs from distillation, in affording a solid product, while the
fatter yields a condensed liquid. In this mode, sulphur may,
in part, be purified ; and its purification is completed, by
boiling it repeatedly in distilled water ; then in twice or thrice
its weight of nitro-muriatic acid, diluted with one part of dis¬
tilled water; and, finally, by washing it with distilled water,
2
SECT. I.
SULPHUR.
331
till this comes off tasteless, and incapable of changing the
blue colours of vegetables.
V. When flowers of sulphur are digested in alcohol, no
union takes place ; but if the two bodies be brought into contact,
when both are in a state of vapour, they enter into chemical
union. This may be shown by an ingenious experiment of
La Grange, the apparatus for performing which is represented
in the first plate of his “ Manual.” Into a glass alembic
(see the plates to this work, fig. 2) put a little sulphur; over
this suspend a small bottle filled with alcohol ; and apply a
receiver to the pipe of the alembic, the head being put into
its place. Lute the junctures, and apply a gentle heat to the
alembic. The sulphur will now be raised in vapour ; and the
vapour surrounding the bottle of alcohol, the latter will be
volatilized, and will meet in this state the fumes of sulphur.
A combination will take place between the two bodies, and
sulphurized alcohol will pass into the receiver. On pouring
this preparation into water, the sulphur will be precipitated.
VI. Though it had already been suspected (chiefly from the
experiments of M. Berthollet, jun. described in sect. 6, art. 4,
of this chapter) that sulphur contains hydrogen, yet the
first unequivocal evidence of the fact was furnished by Sir H.
Davy. A bent glass tube, having a platinum wire hermeti¬
cally sealed into its upper extremity, was filled with sulphur.
The sulphur was melted by heat ; and a proper connection
being made with the Voltaic apparatus of 500 double plates,
each six inches square and highly charged, a most intense
action took place. A very brilliant light was emitted ; the
sulphur soon entered into ebullition ; elastic matter was
evolved in great quantities ; and the sulphur, from being of a
pure yellow, became of a dark reddish brown tint. The gas
was found to be sulphureted hydrogen, or hydrogen gas hold¬
ing sulphur in solution ; and its quantity, in about two hours,
was more than five times the volume of the sulphur employed.
Another proof of the presence of hydrogen in sulphur is
derived from the action of potassium ; for these two bodies
combine with great energy, and evolve sulphureted hydrygen,
with intense heat and light.
Lastly, when dry sulphur is burned in dry oxygen gas, Sir
SULPHUR.
CHAP. XII.
332
H. Davy is of opinion that, besides sulphuric acid, a portion
of water is also formed ; but he is still doubtful whether the
hydrogen in sulphur can be considered as any thing more than
an accidental ingredient. This view of the subject is em¬
braced, also, by Berzelius *, who found, by heating sulphur
with oxide of lead, that the quantity of water produced is
much too minute to indicate any definite proportion of hydro¬
gen in sulphur.
Another ingredient of sulphur, it appeared probable from
the experiments of Sir H. Davy, is oxygen. For potassium,
after being made to act on sulphureted hydrogen gas, evolved
less hydrogen from water, than it ought to have done. It
has since, however, been proved by Gay Lussac f, that when
all sources of fallacy are avoided, a given weight of potassium,
which has been exposed to sulphureted hydrogen, separates
exactly the same volume of hydrogen gas from water, as an
equal weight of recent metal. Potassium, therefore, acquires
no oxygen from the sulphur, which is contained in sulphur¬
eted hydrogen.
VII. Sulphur is inflammable, and appears susceptible of
two distinct combustions, which take place at different tempe¬
ratures ;f. At 140° or 150° Fahrenheit, it begins sensibly to
attract oxygen; and if the temperature be raised to 180° or
190°, the combination becomes pretty rapid, accompanied by
a faint blue light. But the heat evolved is scarcely sensible ;
at least it is so weak, that the sulphur may thus be burned
out of gunpowder, and the powder be rendered useless with¬
out inflaming it. At a temperature of 300°, its combustion,
though still feeble compared with that of some other bodies, is
much more active, and accompanied with a redder light.
When set on fire in oxygen gas, it burns with a very beauti¬
ful and brilliant light; but of a given quantity of oxygen gas,
it is not possible to condense the whole by this combustion,
for reasons which hereafter will be stated. The product of
these combustions, when examined, will be found to be sul-
* 79 Ann. de Chiin. 119. f Ann. de Chim. vol. Ixxiii.
X l or an account of the oxides of sulphur, see Dr. Thomson's paper in
Nicholson's Journal, vi. 101.
SECT. II.
SULPHURIC ACID.
333
phurous and sulphuric acid, but chiefly the former, and if
water be carefully excluded, sulphurous acid only is formed.
It is necessary, therefore, in order to produce sulphuric acid,
to make the experiment over water.
SECTION II.
Sulphuric Acid .
The properties of this acid must be exhibited by a portion
of that usually found in the shops. They are as follows :
(a) Sulphuric acid has a thick and oily consistence ; as may
be seen by pouring it from one vessel into other.
(b) In a pure state, it is perfectly limpid and colourless.
(c) When mixed suddenly with water, considerable heat is
produced. Four parts, by weight, of concentrated sulphuric
acid, and one of water, when mixed together, each at the
temperature of 50° Fahrenheit, have their temperature raised
to 300°. When an ounce of water has been suddenly mixed
with three of sulphuric acid, and the mixture been suffered
to cool to the temperature of the atmosphere, an additional
half oz. of water raises it to 86°, a second to 96°, and a third
to 1 01° The greatest elevation of temperature, Dr. Ure
finds to be occasioned by the sudden mixture of 73 parts by
weight of strong sulphuric acid with 27 of water. This rise of
temperature takes place, because the affinity or capacity of the
compound of sulphuric acid and water for caloric, is less than
that of the acid and water separately. A diminution of bulk
also ensues ; that is, one measure of acid and one of water do
not occupy the space of two measures, but about ^L-th less ;
and the greatest condensation results, when those proportions
are used, which give the greatest increase of temperature.
Owing to the heat produced by its admixture with water, the
dilution, for ordinary purposes, should be conducted very
gradually; and the acid should be added to the water by small
portions at once, allowing each portion to cool before a fresh
addition is made. On the principle of its attraction for wrater
* Philips on the London Pharmac. p. 24.
334
SULPHURIC ACID.
CHAP. XII.
is to be explained, also, the rapid increase of weight which the
acid requires when exposed to air. In one day, three parts
of sulphuric acid, exposed to the atmosphere, are increased in
weight one part; and one ounce, by twelve months’ exposure,
has been found to gain an addition of 6f-.
(d) Perfectly pure sulphuric acid remains quite limpid dur¬
ing dilution. The sulphuric acid, however, commonly found
in the shops, under the name of oil of vitriol, on admixture
with water, deposits a white powder, in considerable quantity,
consisting of various impurities, but chiefly of sulphate of
lead. Berzelius has found, also, a minute quantity of titanium
in sulphuric acid of English manufacture, and tellurium
in acid prepared at Stockholm #. By evaporating sulphuric
acid of commerce in a platinum dish, Dr. Ure has obtained
from one half to three quarters of a grain in 100 of solid mat¬
ter, consisting of about two parts of sulphate of potash and
one of sulphate of lead f .
(e) Sulphuric acid is nearly twice as heavy as water. The
specific gravity of the strongest pure acid that can be obtained,
is 1.850; but even this contains 19 (according to Dr. Wollas¬
ton, 18.44) per cent, of wrater, which appears essential to its
constitution, and can only be separated by combining the acid
with a base. Dr. Ure states that genuine commercial acid
should not exceed 1.8485. When denser, its purity may be
suspected. It has been ascertained, by Mr. Dalton, that acid,
of nearly the maximum strength, has its specific gravity very
little altered, by adding or subtracting small portions of wa¬
ter. Thus acids, containing 81 and 80 per cent, of acid, do
not differ more than 1 in the third place of decimals ; nor is the
specific gravity proportionally changed by dilution till it falls
as lowr as 1.78. The strength of the more concentrated acid
may be better ascertained, by observing how much water is
required, to bring it down to the specific gravity 1.78. The
boiling point, also, Mr. Dalton has discovered, is a much bet¬
ter test of its strength ; and he has constructed the following
useful Table, in which account is taken of all these circum¬
stances.
f Journ. of Science, iv. 115.
* Thomson’s Annals, x. 464.
SECT, IK
SULPHURIC ACID.
S 35
Mr. Dalton's Table of the Quantity of real Acid in 100 Parts of
Liquid Sulphuric Acid , at the Temperature 60° Fahrenheit .
Atoms
Acid Water.
Real Acid
per cent, by
Weight.
O
Real Acid
per cent, by
Measure.
Specific
Gravity.
Boiling Point.
1+0
100
unknown.
unknown.
unknown.
1+0
81
150
1.850
620°
80
148
1.849
605°
79
146
1.848
590°
78
144
1.847
575°
77
142
1.845
560°
76
140
1.842
545°
75
138
1.838
530°
74
135
1.833
515°
73
133
1.827
501°
72
131
1.819
487°
71
129
1.810
473°
70
126
1.801
460°
69
124
1.791
447°
i 4- 2
68
121
1.780
435°
67
118
1.769
422°
66
116
1.757
410°
65
113
1.744
400°
64
111
1.730
391°
63
108
1.715
382°
62
105
1.699
374°
61
103
1.684
367°
60
100
1.970
360°
l + 3
58.6
97
1.650
350°
50
76
1.520
290°
40
56
1.408
260°
1 +10
30
39
1.30 +
240°
1 +17
20
24
1.200
224°
1+38
10
11
1.10-
218°
It has been ascertained by Dr. Ure that by adding about
2T per cent, of its weight of sulphate of potash to concen¬
trated oil of vitriol, its specific gravity may be increased to
1,860. The only mode, therefore, of ascertaining exactly the
strength of oil of vitriol is by saturating a known quantity with
an alkali ; and it may be assumed as sufficiently correct, that
336
SULPHURIC ACID.
CHAP. XII,
100 grains of dry sub-carbonate of soda neutralize 92 grains of
pure liquid sulphuric acid ; or that 100 grains of the acid re¬
quire 108, or 108.5, of the sub-carbonate for saturation.
It is sometimes of importance to the chemical artist to know
the proportion, not of real acid , but of acid of commerce , in
diluted sulphuric acid of different specific gravities. An ap¬
proximation to the true proportion may be obtained, by in¬
creasing the numbers, indicating the real acid, one fourth. For
example, acid of the specific gravity 1 .200, contains according
to the above table, 20 per cent, of real acid ; which, increased
one fourth, gives 25 per cent. Gf acid of sp. gr. 1.849. A very
copious 'Fable of the quantities of sulphuric acid of commerce
in acid of different densities, constructed by Mr. Parkes from
actual experiment, is given in the 40th volume of the Philoso¬
phical Magazine, and in vol. ii. of his Chemical Essays, p. 144.
Its length only prevents me from inserting it here. The shorter
Table of Vauquelin, in the 30th volume of Nicholson’s Jour¬
nal, is rendered less fit for the English chemist, because the
acid, employed in the experiments on which it is founded,
is inferior in density to the average acid sold in this country.
In taking the specific gravity of sulphuric acid, it is of import¬
ance to attend to its temperature #, which must be examined
by a thermometer, having its bulb perfectly dry. According
to Dr. Ure, 10° Fahrenheit make a difference in the density
of oil of vitriol of 0.005. With due attention to this, and
other necessary precautions, Dr. Ure has constructed a Table,
which, as it is of moderate length, and exhibits at one view
the proportion not only of real or dry acid, but of liquid acid,
in sulphuric acid of different specific gravities, I shall insert
in the Appendix. In the memoir of which the Table forms
a part, Dr. Ure has endeavoured to established some general
formulas for calculating the proportion of oil of vitriol in di¬
lute acid of any specific gravity, and also for finding the spe¬
cific gravity corresponding to a given proportion of acid f .
(f) Sulphuric acid, by a sufficient reduction of its tempe¬
rature, may be frozen ; and under favourable circumstances,
it assumes a regular crystalline form, a considerable degree of
* See Park es’s Essays, ii. 461.
f Journ, of Science, iv. 127.
t SECT. II.
SULPHURIC ACID.
337
t solidity or hardness, and a density exceeding that which it
J possessed in a fluid state. From the experiments of Mr.
Keir * it follows that there is a certain point of specific gra-
’ vity (viz. 1780 to 1000), at which the sulphuric acid most
readily congeals ; and when of this degree of strength it re-
! quires even a less degree of cold than is sufficient to freeze
’ water, its congelation taking place at 45° Fahrenheit. From
i the specific gravity of 1786 on the one hand to 1775 on the
» other, it freezes at 32° Fahrenheit. It is singular that it re«
i mains congealed at a temperature higher than that originally
j required for freezing it Acid, for example, which did not
become solid till its temperature was reduced to 32°, remains
‘j frozen at 45°. When of the specific gravity of 1 843, or as
! nearly as possible of that of commerce, it was found by Mr.
I Macnab f to freeze at —15° Fahrenheit; but this acid, mixed
i with rather more than half its weight of water required for
: congelation the temperature of —36° Fahrenheit.
(g) To purify sulphuric acid, it must be distilled in a glass
o retort, placed in the sand-bed of a reverberatory furnace.
I This process is a difficult one. But to those who have sufli-
: cienfc experience in chemical operations, the following instruc-
ij ti'ons may be useful ; especially as it is indispensable, in all
t experiments of research, to employ an acid purified by distil-
a lation.
The furnace, in which this process is conducted, should
I have a contrivance for supporting a sand bath within it at a
: proper height ; and an opening in the side, for transmitting
the neck of the retort. (PI. vii. fig. 62, 63.) The retort must
t be coated with clay and sand over its whole body, and also
i over that part of the neck which is exposed to the fire. It is
I; then to be placed, the coating being previously dry, in the
7 sand-bath, about one half filled with sulphuric acid ; and a
receiver must be applied, but not kited on. The fire must
[ now be lighted, and raised with extreme caution. The first
: portion that comes over, amounting to about one sixth, con-
g sists chiefly of water, and may be rejected. This is followed
; by the concentrated acid ; and, at this period, there is great
* Philosophical Transactions, Ixxvii. 267. + Ibid, lxxvi. 24L
VOL. T. Z
\
538
SULPHURIC ACID.
CHAP. xire
risk that the neck of the retort will be broken, by the contact
of the condensed acid, which has a very high temperature,
and which frequently cracks the glass, as effectually as the
application of a red-hot iron. The fire must be regulated by
the register door of the ash-pit, so that several seconds may
elapse between the fall of the drops into the receiver. The
process may be continued as long as any acid is condensed.
The retorts, employed for this purpose, should be most atten¬
tively annealed.
The difficulty of rectifying sulphuric acid is much diminished,
by using a retort of the capacity of from two to four quarts
when a pint of the acid is employed, and by connecting its
neck with the receiver by means of an adopter three or four
feet long. The retort may be set over a charcoal fire, and
the flame made to play gently on its bottom. No luting is to
be employed, and the receiver is to be surrounded with cold
water. With this arrangement, and a cautious regulation of
the heat, Dr. Ure finds that sulphuric acid may be distilled
without much risk, in a continuous gentle stream *.
Sulphuric acid may be less perfectly purified by diluting it
with an equal weight of water, allowing the impurities to settle,
decanting the clear liquor, and evaporating it to the proper
degree in a glass retort.
(/i) The proportion of the elements of sulphuric acid has
been investigated by several chemists. Bertliollet oxygenated
17.846 parts of sulphur by nitric acid, and obtained a quan¬
tity of sulphuric acid, which gave 127.515 parts of sulphate
of barytes. Hence 100 parts of sulphur would have formed
230.79 parts of real sulphuric acid (= about 292 of density
1.85); but this product falls short of what ought to have re¬
sulted. Klaproth, Richter, and Bucholz obtained results
nearly agreeing with each other. Berzelius, to avoid all fal¬
lacy from the hydrogen contained in sulphur, combined it, in
the first place, with lead, which, like other metals, always
evolves much hydrogen, and then oxygenated the sulphuret.
The following Table exhibits the proportions, deduced from
different experiments, in 100 parts of real acid:
* Journal of Science, iv. 116.
SECT* Ho SULPHURIC ACID* S39
Sulphur. Oxygen,
From the experiments of Berthollet . . 43.28 . . 56.72
- — _____ - _ — - — Klaproth * . 42,20 . . 57.80
- — — - - - — - - Bucholz * . . 42.50 . . 57.50
______ - - — _ — - - Berzelius . . 39.92 . . 60.08
Proportions admitted by Dr. Wollaston . . 40.0 . . 60.0
If the proportions be taken at 4o sulphur and 60 oxygen*
and if the acid consists, as Mr. Dalton supposes, of 1 atom
of sulphur and 3 atoms of oxygen, the atom of sulphur will
weigh 15; for as (60 3 =) 20 is to 40 so is 7.5 to 15; and
the weight of an atom of sulphuric acid will be 37.5. Mr*
Dalton’s numbers are 13 for the atom of sulphur, and 34 for
that of sulphuric acid; the difference being occasioned by his
taking oxygen at 7, instead of 7.5.
A coincidence has been pointed out by Berzelius, which is
very remarkable, and is deemed by him sufficiently general,
to be admitted as a law ; viz. that in any combination of two
oxygenated bodies with each other, the oxygen of the one is
either a multiple or divisor of that of the other, by some sim¬
ple number. Sulphuric acid, of 1850 density, affords an illus¬
tration of this principle ; for it consists of 8 1 real acid and ] 9
water; and it will be found that the oxygen in the acid is, as
nearly as possible, 48; and the oxygen in the water 16, so
that in this case the multiple is 3, for 16 x 3 = 48. Various
other examples of the same general principle will be given, in
treating of metallic oxides. In all neutral compounds of sul¬
phuric acid with alkaline, earthy or metallic bases, the acid
contains a quantity of oxygen, which exceeds that in the base
by the same multiple 3.
(i) Sulphuric acid is decomposed at the temperature of the
atmosphere, by inflammable substances, and acquires a dark
colour. The addition of a little brown sugar, or a drop of
olive oil, to a portion of the acid, imparts to it a brownish
hue, which in time changes to black. Hence this acid should
always be kept in bottles with glass stoppers ; for a small bit
of straw or cork, if dropped into a considerable quantity oi sul¬
phuric acid, changes it in the manner that has been pointed out*
(k) In high temperatures, sulphuric acid is still farther de¬
composed by combustible bodies.
z 2
SULPHURIC A CTi>.
CHAP. XIEr
540
1. Hydrogen gas, brought into contact with sulphuric acid,
in a state approaching ignition, decomposes it, and water and
sulphurous acid are formed. This, however, is a most dan¬
gerous and difficult process, which it is not adviseable to re¬
peat.
2. According to Gay Lussac, sulphuric acid is decomposed
by heat alone, and is resolved into two parts by measure of
sulphurous acid gas, and one of oxygen gas. This experiment
is best performed by passing the acid through a red-hot tube
of glass or porcelain.
3. Sulphur, by being boiled in sulphuric acid, parity de¬
oxygenates it, and converts a portion of it into sulphurous acid,
which comes over in a gaseous state.
4. Into a glass retort, put such a quantity of sulphuric acid
as will fill about one fourth part of it, and add a small portion
of powdered charcoal. On applying the heat of a lamp, gas
will be produced very abundantly. Let this gas be conveyed
by a tube fixed to the mouth of a retort, and bent in the
proper manner, into an inverted jar of water; or, if it can be
had, into an inverted jar of quicksilver in a mercurial appa¬
ratus. During this operation, the carbon attracts part of the
oxygen of the sulphuric acid, and forms carbonic acid gas.
But the sulphur is not entirety disoxygenated ; and a com¬
pound is therefore formed of sulphur and oxygen, containing
less oxygen than the sulphuric acid. This compound exists
in the state of a gas, and its properties may next be examined.
To avoid, however, the complication which the admixture of
carbonic acid with this new product introduces into the expe¬
riment, it may be proper to prepare it in a mode less objec¬
tionable, but the rationale of which cannot at present be ex¬
plained. This consists in dissolving two parts, by weight, of
quicksilver in one of sulphuric acid, and boiling the mass to
dryness, in the bottom of a broken Florence flask. The dried
mass is next to be distilled in a strong sand- heat; a glass
globe being interposed between the retort and the receiving
mercurial trough, to condense any sulphuric acid that may
escape decomposition. (See pi. iii. fig. 31.) The gas thus
obtained is termed, conformably to the principles of the new
nomenclature, sulphurous add.
SECT. III.
SULPHUROUS ACID GAS*
341
SECTION III.
Sulphurous Acid Gas .
Sulphurous acid may be formed, also, 1st, by burning
sulphur at a low temperature in common air, under a glass
bell ; and if slips of linen cloth, dipped in a solution of potash,
be exposed to the vapour, the alkali forms a combination with
the sulphurous acid, which may afterwards be washed off and
evaporated. The dry salt, distilled with liquid tartaric acid,
gives sulphurous acid gas.
2dly. It is formed, exclusively, when sulphur is burned in
dry oxygen gas. The gas, when restored to its original tem¬
perature, is found to be contracted Tyth 0r -Hyth of its bulk ;
but this is probably owing to the hydrogen contained in sul¬
phur, for there is every reason to believe that oxygen gas, by
becoming sulphurous acid, is not at all changed in volume.
3dly. It is produced, by heating red oxide of mercury with
one fourth of its weight of sulphur, in the proportion of about
a cubic inch for every five grains of the oxide.
Its properties are the following :
(a) It has a pungent and suffocating smell, exactly resem¬
bling that which arises from burning sulphur.
(5) It is more than twice as heavy as atmospherical air.
One hundred cubic inches are stated by Mr. Kirwan to weigh
70.215 grains, which would make its specific gravity 2.265.
By Sir H, Davy, the same volume is said to w7eigh 68 grains,
which would give the specific gravity of 2.23. According to
a calculation of Gay Lussac, founded on the proportion of
its elements, its specific gravity should be 2.30314. Berzelius
finds it by experiment to be 2.247 *.
(c) Monge and Clouet assert, that if the gas be exposed, at
the same time, to a temperature of 31° Fahrenheit, and to
great pressure, it assumes a fluid state.
(d) It extinguishes burning bodies ; and kills animals, when
respired.
* Ann. de Chim, et Phys. v. 1?3.
$4f% SULPHUROUS ACID GAS, CHAP. Xljf*
(e) It has the property of whitening or bleaching silk, and
of giving it lustre.
(/) Of sulphurous acid, water absorbs 33 times its bulk,
or one eleventh of its weight, caloric is evolved, and the solu-
tion at 68° has the specific gravity 1.0513. Mr. Dalton states
the quantity absorbed to be only 22 times the bulk of the
water. From the solution, when recently prepared, the gas
may be separated by heat, but not by congelation.
(g) The watery solution does not redden infusion of litmus,
as acids in general do, but totally destroys its colour. Hence
its use in bleaching several vegetable and animal products,
It. restores the colour of syrup of violets, which has been red¬
dened by other acids
(h) Sulphuric acid, saturated with this gas, which may be
effected by passing the gas through the acid, acquires a strong
smell, a yellowish brown colour, smokes when exposed to the
air, and has the property of assuming a solid form, by a mo¬
derate reduction of its temperature. When distilled, the first
product, which is a compound of the two acids, assumes a
solid form. It has been called glacial sulphuric acicl. It has
however, been asserted by Vogel f, that the presence of sul¬
phurous acid is not the cause of the glacial quality of oil of
vitriol ; and that, when converted to this state, by boiling in
contact with sulphur, it contains no sulphurous acid. The
nature of the change he has not yet fully explained.
(£) Sulphurous acid is absorbed by crystallized borax, and
by means of this property, Cluzel observes, may be separated
from carbonic acid, and some other gases f .
Sulphurous acid is again converted to the state of sulphuric,
by restoring oxygen to it.
I. A mixture of oxygen and sulphuric acid gases, both
perfectly dry, and standing over mercury, is not diminished
by remaining in contact with each other during some months;
but if a small quantity of water be added, the mixture begins
to diminish, and sulphuric acid is formed. The same gases
* Nicholson’s Journal, xvii. 303.
| 83 Ann. de Chim. 259»
f 84 Ann. de Chim. 283.
SECT. III.
SULPHUROUS ACID GAS
343
in a state of mixture., by the action of electricity* or by being
driven through a red-hot porcelain tube, afford sulphuric acid.
The proportions required for mutual saturation are two mea¬
sures of sulphurous acid and one of oxygen gas.
2. To a portion of water saturated with sulphurous acid
gas add a little oxide of manganese, a substance that contains
much oxygen, loosely combined. The pungent smell of the
water, and the other characteristics of sulphurous acid, will
soon disappear.
3. Sulphurous acid gas is condensed into sulphuric acid by
admixture with nitrous gas, and also by oxymuriatic acid gas;
but not unless the gases are in contact with water.
( k ) When the temperature of sulphurous acid gas is greatly
reduced, by surrounding it with a mixture of snow and mu¬
riate of lime, it is changed into a liquid.
(/) If sulphurous acid gas and fresh muriate of tin are
brought into contact over mercury, the volume of the gas is
speedily diminished, sulphur is deposited, and the pro-mu¬
riate becomes a per-muriate of tin. (Accum.)
(m) It is decomposed, when submitted to the heat of igni¬
tion, in contact with certain combustible bodies. Thus, when
a mixture of sulphurous acid and hydrogen gases are driven
through a red-hot porcelain tube, the oxygen of the acid
combines with the hydrogen, and forms water* and sulphur is
obtained in a separate form. The sulphurous acid is decom¬
posed, also, when transmitted over red-hot charcoal ; and, as
appears from Gay Lussac’s experiment, by potassium.
From the testimony of the same chemist we learn that 100
parts of sulphur, to become sulphurous acid, unite with 95
oxygen. The following Table shows the numbers derived
from different authorities. Sulphurous acid contains per cent.
Sulphur. Oxygen.
According to Gay Lussac .... 51.30 ...... 48.70
- - - Berzelius ...... 50.03 . . .... 49.07
— — — Thomson . . 53.0 ...... 47.0
The determination of Berzelius, of equal weights of its
ingredients, agrees best with the specific gravity of the gas ;
for if 100 cubic inches weigh 68, and 100 cubic inches of
344
SULPHATES.
CHAP. XII.
oxygen 34, the remaining 34 must consist of sulphur. Its
atomic constitution, according to Mr. Dalton, is ! atom of
sulphur + 2 atoms of oxygen ; and the weight of its atom
will, therefore, be 30.
The combination of 1 atom of sulphur with I atom of oxy¬
gen constitutes probably the acid, which is formed in solutions
of alkaline sulphurets by exposure to the atmosphere. Of
this, which has been called hypo-sulphur (ms acid , the little that
is known will be found under the article sulphurets ; but it has
not yet been obtained in an uncombined state*
SECTION IV.
t
Cmnbination of Sulphuric Acid with Alkalies »
Art. I.-— Sulphate of Potash .
This salt may be formed by saturating the carbonate of
potash with sulphuric acid, and crystallizing the solution* Its
properties are the following :
(a) It crystallizes in small six-sided prisms, terminated by
six-sided pyramids with triangular faces. Its specific gravity,
according to Hassenfratz, is 2.0478.
(b) It has a bitter taste.
(c) It decrepitates when thrown on a red-hot iron, or on
red-hot coals, and is volatilized by a strong heat, first running
into fusion. By a low red heat it loses very little of its w’eight,
not more than one and a half or two per cent. Indeed it does
not essentially contain any water.
(d) Water, at 60° of Fahrenheit, takes up only one six¬
teenth of its weight ; but boiling water dissolves one fifth, or
by continuing the application of heat even one fourth.
(e) The composition of this salt is determined by the quan¬
tity of sulphate of barytes, which its solution affords when
decomposed by any barytic salt. From 100 parts of the ig¬
nited salt, dissolved in water, Dr. Marcet obtained 132 of
sulphate of barytes, Berzelius 134.68, and Mr. R. Phillips,
1 35.7. Hence the composition of the salt (reckoning the acid
in sulphate of barytes at 33.5 per cent.) is,
SECT. IV.
SULPHATE OF POTASH.
345
Acid,, Base.
According to Dr. Marcet .... 44.22 ...... 55.78
Mr. Phillips .... 45.79 ...... 54,21
Bucholz ........ 46.21 ...... 53. 79
_____ Dalton ........ 44.70 ...... 55.30
- • - Berard ........ 42.76 ...... 57.24
__________ Berzelius ...... 45.0 ...... 55.0
Dr. "Lire ........ 45.5 . , .... 54.5
If the weight of the atom of potash be 50;, and that of
sulphuric acid 37.5, the determination of Berard would be
nearest the truth ; but the proportions which would best suit
the weights assigned by Mr. Dalton (42 for potash and 54 for
sulphuric acid), are those approaching to 45 acid and 55 base®
For though some doubt may exist as to the precise weights of
the atoms of potash and sulphuric acid, it can scarcely be
questioned that this salt is composed of one atom of potash
united with one atom of acid. Mr. Dalton's numbers make
i the weight of the atom 76, and the corrected ones would in¬
crease it to 87 .5.
(f) Sulphate of potash is decomposed, in high tempera-
1 lures, by charcoal. Mix any quantity of the salt with one
fifth of its weight of charcoal finely powdered, and expose the
mixture, in a crucible, to a strong; heat,. The carbon will
unite with the oxygen of the sulphuric acid, and will escape
in the state of a gas. What remains is a compound, here-
t after to be described, of sulphur and potash, or more pro*
bably of sulphur and potassium No change is Effected in
sulphate of potash by fusion with sulphur, which sublimes
unaltered f .
Bi-sulphate of Potash „
When to a saturated solution of sulphate of potash in boil¬
ing water, we add an excess of sulphuric acid, the first crys¬
tals, which are formed, contain a considerable excess of sul¬
phuric acid, not less in the whole, according to Berthollet :jg
than 55,8 per cent. By continuing to evaporate the solution.
* Vauquelin, Ann. de Chim. etPhvs. v. 31.
7 Memoires d’Arcneil, ii. 180.
f Ibid. p. 20,
346
SULPHATES.
CHAP. XII,
we obtain successive quantities of crystals, which hold less and
less acid in combination. Tims the second set, according to
the same chemist, contain only 49.5 per cent, of acid; and he
was therefore of opinion, that sulphuric acid and potash are
capable of uniting in all proportions. It is much more agree¬
able, however, to analogy to believe, that in this, as in all
other energetic combinations, the proportions are limited.
The bi-sulphate or super-sulphate, it is probable, consists of
one atom of base with two atoms of acid, or of 55 base + 90
acid ; and its composition may be contrasted with that of the
sulphate as follows :
Bi-sulphate . Sulphate.
Potash .......
100 . .
• • ■£) • • • 9
100
Sulphuric acid
. . 62 ....
164 . .
82
100
264
100
182
This salt has an intensely sour taste, and a powerful action
on blue vegetable colours. One part is soluble in two of
water at 60°, and in less than an equal weight at 212°. It is
insoluble in alcohol.
Art. 2 . — Sulphate of Soda .
{a) This salt forms regular octahedral crystals, of a pris¬
matic or cuneiform figure ; the two terminating pyramids of
which are truncated near their basis.
( h ) It has a more bitter taste than the preceding sulphate,
and melts more easily in the mouth.
(c) It swells upon a heated iron, in consequence of the loss
of its water of crystallization, and a white powder is left,
amounting to only about 36 parts from 100 of the original
salt, or 43.2 according to Bucholz.
( d ) By exposure to the atmosphere, it effloresces, and loses
weight, and with so much quickness, that it is difficult to
ascertain precisely its water of crystallization. Berzelius states
it at 56 per cent.
(e) It is very soluble in water, three parts of which, at 60c
of temperature, dissolve one of the salt; and boiling water
dissolves its own weight.
SECT. IV.
SULPHATE OF SODA.
(f) Its composition is inferred from the quantity of sul¬
phates of barytes, obtained by decomposing the solution of a
known weight of this salt by any barytic salt. Bucholz, from
1000 grains of the crystallized salt (= 432 deprived of water)
obtained 698 of sulphate of barytes ; and Berzelius, from 5
parts of the dry salt, precipitated 8.16 of sulphate of barytes.
His experiment, to have corresponded with that of Bucholz,
should have given 8.12. Assuming the acid in sulphate of
barytes to be 3 3.5 per cent, 100 parts of dry sulphate of soda
(giving 161.3 of the barytic sulphate) must consist of
Base 46 ..<«.•«. 1 00
Acid ........ 54 ....... . 1 1 7.5
100
Mr. Dalton's numbers are 54.8 acid -f- 45.2 base; Dr.
Wollaston’s 56 + 44 ; Dr. Ure's 55.55 + 44.45 ; and those
of Berzelius 55.76 + 44.24. But whichever of these num¬
bers may be adopted, it will be found not inconsistent with
the opinion, that the salt is composed of one atom of base *f
one atom of acid.
The crystallized sulphate consists, calculating from the data
furnished by Berzelius, of
Soda ........ 39.36
Acid ........ 24.64
Water . 56.
100.
Art. 3.- Sulphate of Ammonia .
Sulphate of Ammonia may be composed by adding sub¬
carbonate of ammonia to dilute sulphuric acid; 100 parts of
the compact sub-carbonate requiring, according to Dr. Ure,
I 88 concentrated sulphuric acid.
(a) The sulphate of ammonia forms long flattened prisms
with six sides, terminated by six-sided pyramids.
(5) It slightly attracts moisture from the air.
(c) It has a cool bitter taste.
348
SULPHATES,
CHAP. XII,
(d) Two parts of water, at 60°, take up one of the salt,
and boiling water dissolves its own weight. During solution,
it produces cold ; and also when mingled with powdered ice,
or with snow.
(<?) The sublimed salt has an excess of acid ; a portion of
the base being expelled by the application of heat.
(,/) It contains, per cent., according to Berzelius,
Ammonia ...... 22.6
Sulph. acid ..... 53.1
Water ......... 24.3
100.
When dried as completely as possible without decomposing:
it, Dr. lire found this salt to consist of 61 acid -f 39 base,
which base was itself constituted of 25.96 ammonia and 1 3.04?
water. According to Dr. Wollaston’s scale of equivalents,
the numbers are 61 acid, 26^ ammonia, and 13f water*.
(g) Sulphate of ammonia liquefies, by a gentle heat, and is
volatilized. If a little stronger heat be applied, it is decom¬
posed f , and hence great care is required in drying it.
(k) The pure fixed alkalies, potash, and soda, seize the
sulphuric acid, and set at liberty the alkali. Hence a strong
smell of ammonia arises on the admixture of pure soda or
potash with this salt.
Art. 4. — Sulphate of Barytes .
Barytes has a powerful affinity for sulphuric acid ; and the
combination of these two bodies may be effected with great
facility.
(a) To a solution of pure barytes, add sulphuric acid. A
white precipitate will apppear, which is the sulphate of barytes.
( h ) The same compound is formed, by adding sulphuric
acid to carbonate of barytes, or to a solution of muriate or
nitrate of barytes.
* Thomson’s Armais, x. 205.
f See Mr. Hatchett’s paper in Philosophical Transactions, 1796, or
Davy’s Researches.
SECT. IV.
SULPHATE OF BARYTES.
349
(c) The sulphate of barytes is one of the most insoluble
substances, requiring for its solution 43,000 times its weight
of water.
(d) Barytes has a stronger affinity than any other body for
sulphuric acid.
(<?) Owing to these properties the solutions of pure barytes,
and of the nitrate and muriate of barytes, are very sensible
tests of sulphuric acid, and of all its combinations. Let a
single drop of sulphuric acid fall into a wine quart of pure
distilled water. On adding a few drops of one of the fore-
going solutions of barytes, a precipitation will ensue.
(f) Sulphate of barytes is decomposed by carbonate and
sub-carbonate of potash. Boil the powdered sulphate with a
solution of twice or three times its weight of sub-carbonate of
potash. The carbonic acid will pass to the barytes, and the
sulphuric to the potash.
Some curious facts respecting this decomposition have been
ascertained by Mr. Richard Phillips*. When sulphate
of barytes is boiled, for two hours, in contact with pre¬
cisely its equivalent quantity of sub- carbonate of potash,
(that is, with the quantity which ought to produce entire de¬
composition), only one fourth of the sulphate of barytes is
converted into carbonate. Reversing the process, and boiling
together equivalent quantities of carbonate of barytes and
sulphate of potash (the mutual decomposition of which could
not have been expected from the established order of affinities)
it was found that, out of 85 parts of carbonate of barytes, 57
had been changed into sulphate. It is obvious, therefore,
that the entire decomposition of sulphate of barytes by car¬
bonate of potash can never be expected, so long as the car¬
bonate of barytes, formed by the mutual action oi these two
salts, remains in contact with the sulphate of potash gene¬
rated at the same time; for this will re-convert the carbonate
of barytes into sulphate. Nor will any quantity of carbonate
of potash, that can be employed, be adequate to the entire
decomposition of the sulphate of barytes.
( g ) By this process carbonate of barytes may, however, be
* Journal of Science, &c. i. 80.
$50
SULPHATES.
CHAP. XI r.
procured in sufficient quantity for the purpose of preparing
the pure earth, and its various salts, when the native carbo¬
nate cannot be had in sufficient abundance. The sulphate is
found, in considerable masses, accompanying lead ore, in
Derbyshire and other parts of England, where it is known by
the names of cawk, ponderous spar, &c. When applied to
the purpose of obtaining the carbonate of barytes, it is to be
finely powdered, mixed with three or four times its weight of
sub-carbonate of potash, and boiled with a proper quantity of
water for a considerable time, in an iron kettle, stirring it,
and breaking down the hard lumps, into which it is apt to run,
by an iron pestle. It is then to be washed with boiling water,
as long as this acquires any taste. On the addition of dilute
muriatic acid, a violent effervescence will ensue, and a consi¬
derable portion of the earth, probably along with some metals,
will be dissolved. To the saturated solution, add solution of
pure ammonia, or, in preference, a solution of pure barytes
in water, as long as it disturbs the transparency of the liquor.
This will throw down any metals that may be present ; and
the barytes may afterwards be precipitated in the state of a
carbonate, by a solution of carbonate of potash. Let the
precipitated earth be v/ell washed with distilled water ; and if
the pure barytes is to be obtained from it, let it be treated as
directed, chap. x.
( h ) Sulphate of barytes is also decomposed when ignited
with powdered charcoal, which abstracts the oxygen of the
sulphuric acid, and leaves a combination of sulphur and
barytes. From this, the barytes may be removed by muriatic
acid, as already directed, and the muriatic solution be decom¬
posed by carbonate of potash.
(i) The sulphate ol barytes, when decomposed by charcoal,
affords one variety of solar phosphorus. This phosphorus
has been called, from the place where the sulphate is found
from which it was first prepared, the Bolognian phosphorus.
The native sulphate, powdered after being ignited, and finely
sifted, is to be formed into a paste with mucilage of gum ara¬
ble, and divided into cylinders or pieces of one fourth of an
inch in thickness. These, after being dried in a moderate
heat, are to be exposed to the temperature of a wind furnace,
SECT. IV.
SULPHATE OF STRONTITES.
35 1
placed in the midst of the charcoal When the fuel is half
consumed, it must be replenished, and suffered to burn out
The pieces will be found, retaining their original shapes,
among the ashes, from which they may be separated by the
blast of a pair of bellows. They must be preserved in a well-
stopped phial.
This phosphorus, after being exposed a few minutes to the
sun’s rays, shines in the dark sufficiently to render visible the
dial of a watch. This property is lost by repeated use, in
consequence of the oxygenation of the sulphur ; but may be
restored by a second calcination.
(&) Sulphate of barytes, when artificially formed and cal¬
cined, contains in 100 parts,
Base. Acid.
According to Klaproth . . 66.55 .... 33.45
— — — — Mr. A. Aikin* - 66.04 _ 33.96
« — - - - — — Mr. J. Thomson f 66.96.... 33.04
- __ - — Berth ollet | ..... . 66.50 .... 33.50
— — — — Berzelius § ...... 65.69 ...» 34.31
The determination of Berthollet, being nearly a mean of
three, may be considered as sufficiently accurate. Dr. Wol¬
laston assumes 66 parts of base and 34 of acid, as expressing
most correctly its composition. The native sulphate, accord¬
ing to Klaproth, is composed of one third acid and two thirds
base || . Its atomic constitution is one atom of base and one
of acid.
Art. 5 — Sulphate of Strontites .
I. This salt resembles, very nearly, the sulphate of barytes.
It may be formed in a similar manner, by pouring the solu¬
tion of pure strontites into diluted sulphuric acid, or into the
solution of an alkaline sulphate; for it has a stronger affinity
than any of the alkalies for sulphuric acid. It is soluble in
3840 parts of boiling water.
* Nicholson's Journal, xxii. SOI. f Nicholson’s Journal, xxiii. 174.
I Memoires d’Arcueil, ii. ^ 79 Ann ales de Chitme, 133,
I I Contributions, i. 377.
4
35 2
SULPHATES.
CHAP. XII.
IT. The sulphate of strontites is also found native in con¬
siderable quantities ; chiefly at Aust Passage, and at other
places in the neighbourhood of Bristol. As the native car¬
bonate is now becoming scarce, this compound may be advan¬
tageously employed for procuring artificial carbonate of
strontites. This process is precisely similar to that already
described for decomposing the sulphate of barytes. (Art. 4. g.)
According to a considerable majority of the chemists who
have analyzed it, it consists of
Acid ........
.... 100
Strontites . . . .
.. . . 138
100
238
The accuracy of these numbers is admitted by Dr. Wol¬
laston. But Vauquelin has stated, that is is composed of 46
acid and 54 base, and Stromeyer of 43 acid and 57 base.
Art. 6— Sulphate of Lime .
*
I. The sulphate of lime is formed, by adding to the car¬
bonate a sufficient quantity of sulphuric acid; and by gently
calcining the residue, to expel the redundancy of the latter
acid. It is also found native, in great abundance, under the
names of gypsum, plaster of Paris, &c.
II. it has the following properties*
1. It is insipid and free from smell.
2. It is difficultly soluble, requiring 500 times its weight of
cold water, or 450 of hot water.
3. It is fusible by a moderate heat. When sulphate of
lime, which has been dried at 160° Fahrenheit, is exposed
to a low red-heat, it loses 22 (according to Berzelius, and
Bucholz 21) per cent, of its weight, consisting entirely of
water. After calcination. It absorbs water rapidly, and forms
a good cement.
4. It is decomposed by carbonates of alkali, a double ex¬
change of principles ensuing. Hence the milkiness which
ensues on adding carbonate of potash to many spring waters;
the carbonate of lime, which is generated, being less soluble
3
SECT. IV.
SULPHATE OF MAGNESIA.
35 S
than the sulphate. Hence, also, hard waters, which always
contain sulphate of lime in solution, curdle soap, the alkali
of which is detached by the sulphuric acid, and the oil is set
at liberty.
5. It is decomposed by ignition with charcoal, which sepa¬
rates the oxygen of the sulphuric acid, and leaves a combina¬
tion of lime with sulphur.
By dissolving 100 grains of calcined sulphate of lime in
boiling distilled water, and adding muriate of barytes, I ob¬
tained a precipitate, which, when well washed, dried, and
calcined in a low red-heat, weighed 175.9. Hence 100 parts
of calcined sulphate of lime must contain very nearly
Acid. Base.
According to the above experiment .... 59. .... 41
- - — — Thomson and Berzelius . . 58. ... . 42
Klaproth . . 57.68 . . 42.37
_ — — - . — Dalton . . 58.60 . , 41.40
It consists, therefore, of an atom of lime united with an
atom of acid.
Art. 7 . — Sulphate of Magnesia .
I. When highly concentrated sulphuric acid is suddenly
added to fresh prepared and pure magnesia, very great heat
and vapour are excited, and are accompanied frequently with
an extrication of light. This appearance was first observed
by Westrumb.
II. If the carbonate of magnesia be added to diluted sul¬
phuric acid, the carbonic acid is expelled, and a solution of
sulphate of magnesia is formed, which crystallizes on cooling.
Crystals of sulphate of magnesia may also be procured in the
shops, under the name of Epsom salt.
III. These crystals have the following properties:
1. They have the form of small quadrangular prisms, sur¬
mounted. by quadrangular pyramids with dihedral summits.
They undergo no change by exposure to the atmosphere.
2. At the temperature of 60°, this salt is soluble in an equal
weight of cold water, and in three fourths its weight of boil-
VOL. I. 2 A
354
SULPHATES,
CHAP. XII*
ing water, which thus receives an addition of one fourth of
its bulk.
3. When exposed to a low red-heat, it undergoes the wa¬
tery fusion, but is not volatilized. It loses, however, about
one half its weight, which is water of crystallization, and, ac¬
cording to Berzelius, a very minute portion of acid escapes.
4. One hundred grains of sulphate of magnesia, deprived,
by calcination in a low red-heat, of its water of crystallization,
afforded me 200 grains of sulphate of barytes when precipi¬
tated by the muriate of the latter earth. Hence 100 grains {
of dry sulphate of magnesia are composed of 67 acid and 33
magnesia, and the crystallized salt, supposing it to" contain
half its weight of water, will consist in 100 parts of
50 water,
33.5 sulphuric acid,
16.5 magnesia.
Berzelius, from 100 grains of desiccated sulphate of mag¬
nesia, obtained 194.3 of sulphate of barytes. Hence the dry
salt consists of 65.1 acid and 34.9 earth, and its atomic con¬
stitution is one atom of earth + one atom of acid.
5. Its solution is precipitated by carbonates of potash and
of soda ; but not by carbonate of ammonia, unless heat is ap¬
plied. The carbonate of magnesia of the shops is prepared
by mixing together concentrated and hot solutions of carbo¬
nate of potash and sulphate of magnesia. The sulphate of
potash, thus formed, is removed by copious washing with
water, and the carbonate of magnesia is then dried. The
proportions employed are filtered solutions of 4 parts of the
crystallized sulphate, and 3 of the sub-carbonate. One hun¬
dred parts of the desiccated sulphate give about 71 of sub¬
carbonate of magnesia, or about 31.6 of the pure earth.
6. When a dilute solution of carbonate of soda is mixed
with a dilute solution of sulphate of magnesia, and the sub¬
carbonate which is formed, if any, is separated by filtration,
crystals of carbonate of magnesia, after some time, shoot in
the liquid, containing a larger proportion of water, but no
more carbonic acid than the common carbonate, see chap. x.
sect. 4. When solution of pure ammonia is added to that of
SECT. IV. SULPHATE OF ALUMINE AND ALUM. 355
sulphate of magnesia, part of the earth is precipitated. The
rest remains in solution, and, by evaporation, a tripie salt is
formed, consisting of sulphuric acid, magnesia, and ammonia,
and called ammoniaco-magnesian sulphate.
A compound Sulphate of Magnesia and Soda has been de¬
scribed by Dr. Murray, in a note to his paper on the Analysis
of Sea Water *. It crystallizes in rhombs truncated on the
angles and edges ; is soluble in rather more than three times
its weight of water at 60° Fahrenheit ; is permanent in the
air ; and does not fuse, but decrepitates on applying heat. It
is composed of
Sulphate of magnesia 32
Sulphate of soda .................. 39
Water of crystallization . . 29
100.
f
Art. 8 . — Sulphate of Alumine and Alum .
The properties of this salt may be exhibited by those of
the common alum of commerce ; though, as .will afterwards
appear, alum is not merely a combination of this earth with
sulphuric acid ; but is a triple salt, composed either of sul¬
phuric acid, alumine, and potash ; or of sulphuric acid, alu¬
mine, and ammonia. It has the following characters :
(a) It has a sweetish astringent taste. Its specific gravity
is 1.71.
(b) It dissolves in water, five parts of which, at 60°, take
up one of the salt, but hot water dissolves about three fourths
of its weight.
(c) This solution reddens vegetable blue colours; which
proves the acid to be in excess.
(d) When mixed with a solution of carbonate of potash, an
effervescence is produced by the uncombined acid, which also
prevents the first portions of alkali, that are added to a solu¬
tion of sulphate of alumine, from occasioning any precipitate.
( e ) On a farther addition of alkali, the alumine is preci¬
pitated.
* Edinb. Trans.
2 A 2
556
SULPHATES.
CHAP. XII.
(/) Sulphate of alumine, when heated, swells up, loses its
regular form, and becomes a dry spongy mass ; but, according
to Vauquelin #, the whole of its acid cannot be expelled by
heat.
(g) The combination of sulphuric acid with alumine is in¬
capable of crystallizing without an admixture of sulphate of
potash, which forms a constituent of ail the alum of commerce.
According to Vauquelin, 100 parts consist of 49 dry sulphate
of alumine, 7 sulphate of potash, and 44 water. Or 100
grains are composed ol
Acid . . .
. . , . 30.52 . . .
Alumine
. , . . 10.50 . . .
. .. 12 .. .
Potash . .
_ 10.40 . . .
... 9.81
Water . .
. . 48.58 . . .
100.00 f
loot
99.90
The acid, in Vauquelin’s estimate, is evidently rated too
low ; for alum, when precipitated by muriate of barytes, gives,
as nearly as possible, an equal weight of sulphate of barytes,
100 grains of which contain 33.5 of sulphuric acid, the quan¬
tity, therefore, present in 100 parts of alum. According to
Berzelius, alum is composed of
Sulphate of alumine . . 36.85
- - — — — potash . . 18.15
Water . . . 45.
100.
The oxygen of the potash being represented by 1, Berze¬
lius finds that the oxygen of the alumine will be as 3 ; that of
the sulphuric acid as 12 ; and that of the water as 24. The
salt consists, according to Mr. Dalton, of one atom of sul¬
phate of potash, four atoms of sulphate of alumine, and 30
atoms of water. The alumine, he contends, does not exist
in the state of super-sulphate, but of a saturated sulphate, a
salt composed of
* Ann. de Chira. xxxvii. 91. f Vauquelin. J Dalton.
§ Berzelius. In this there is a deficiency of 0.1 per cent.
SECT. IV. SULPHATE OF ALUMINE AND ALUM
Alumine
Acid . .
100
A neutral sulphate of alumine was obtained by Berzelius,
by the following process. He decomposed alum by ammonia;
washed the precipitate, and redissolved it in sulphuric acid.
To the liquor, after evaporation, he added alcohol, which threw
down a sulphate nearly neutral, and rendered perfectly so, by
being washed wdth farther portions of alcohol. Gay Lussac
has also given the following process, communicated to him by
Descotils, for preparing a pure sulphate of alumine. On alum
with base of ammonia, boil nitro-muriatic acid, till all the
ammonia is destroyed, and evaporate to dryness to expel all
the nitric and muriatic acids. The ammonia is decomposed
by the chlorine, wrhich results from the mutual action of those
two acids, and the alumine remains in combination with sul¬
phuric acid only. The saturated solution of this salt in water
is an excellent test to discover potash, for a drop or two added
to a solution of that alkali, or of any of its salts, immediately
causes a precipitation of alum*.
(h) Alum is decomposed by charcoal, which combines with
the oxygen of the sulphuric acid, and leaves the sulphur at¬
tached to the alumine. A combination of alumine, sulphur,
and charcoal, forms the pyrophorus of Homberg . To prepare
this, equal parts of powdered alum and brown sugar are
melted over the fire, and are kept stirring till reduced to dry-
3 ' ness. The mixture, when cold, is to be finely powdered, and
introduced into a common phial, coated with clay, to which
a glass tube, open at each end, is to be luted, to allow the
escape of the gases that are produced. The phial must then
be set in the fire, surrounded by sand, in a crucible. Gas
will issue from the open end of the tube, and may be inflamed
by a lighted paper. When this ceases to escape, the crucible
may be removed from the fire,' and a little moist clay pressed
down upon the open end of the tube, to prevent the access of
air to the contents of the phial. When cold, the tube may
be removed, and a cork substituted in its place. The prin-
* Ann. de Chim. et Phys. vi. 201.
358
SULPHATES.
CHAP. XII.
cipal difficulty in the process, is to stop it precisely at the
period, when the pyrophorus is formed; for it the heat be
continued longer, the preparation will be spoiled.
The pyrophorus thus formed is a black and light powder,
which instantly takes fire when poured out of the bottle into
the air, and inflames suddenly in oxygen gas. Sulphate of
potash appears to be essential to its production, and hence the
sulphuret of potash is a necessary ingredient. From the dis¬
coveries of Sir H. Davy, it appears not improbable that this
pyrophorus may contain sulphuret of potassium. rl he prin¬
cipal part of the phenomena, however, is owing to the com¬
bustion of an extremely light and finely divided charcoal.
Art. 9,— -Sulphate of Glucine .
Glucine combines readily with sulphuric acid, both in its
pure and carbonated state. The resulting salt is extremely
soluble ; insomuch that, when evaporated, it assumes the form
of a syrup, without crystallizing. Its taste is sweet, and
rather astringent. It is decomposed entirely in a high tem¬
perature, the earth being left in a state of purity. It is also
destroyed by ignition with charcoal. It does not yield its
earthy ingredient to any of the acids ; but is decomposed by
all the alkalies and earths, alumine excepted.
Art. 10. — Sulphate of Zircon.
To effect the combination of zircon with any acid, this
earth should be fresh precipitated ; for, after being dried, it
enters with difficulty into union.
The salt, resulting from the union of sulphuric acid with
zircon, is white, insoluble, and without taste. It is decom¬
posed by a high temperature, which expels the acid, and
leaves the zircon pure. It is not changed by other acids, but
yields its sulphuric acid to the alkalies, and to most of the
earths.
Art. 11. — Sulphate of Yttria.
Sulphuric acid readily dissolves yttria, and caloric is evolved
SECT. V.
SULPHITES.
359
during the process. As the solution goes on, the sulphate
crystallizes in small brilliant grains, which have a sweetish
taste, but less decidedly than the sulphate of glucine. Their
colour is a light amethyst red. They require 30 parts of
water, of the temperature of 60°, for solution, and give up
their acid when exposed to a high temperature. They are
decomposed by oxalic acid, prussiate of potash, infusion of
galls, and phosphate of soda.
SECTION V.
Sulphites.
I. The combination of sulphurous acid with alkaline and
earthy bases, may be effected by passing the gas, as it pro¬
ceeds from the materials (sect. 2, A), through the base, dis¬
solved or diffused in water. An intermediate vessel may be
placed, as represented, fig, 30 and 31, to condense any sul¬
phuric acid that may pass over ; and the solution of the alkali
or earth may be contained in a bottle with two necks. Pure
potash, soda, or ammonia, are readily kept in solution : but
barytes or strontites must be dissolved in boiling water ; and
the bottle containing them must be surrounded with hot wa¬
ter, while the gas is transmitted . through the solution. The
solution, when saturated with gas, may be evaporated ; and
this is best done in an alembic, covered with its capital, be¬
cause the salts of this class are changed by the action of the
atmosphere.
II. The sulphites have no peculiarly interesting properties,
that can entitle them to minute and specific description, in a
work devoted solely to the students of chemical science. I
shall enumerate, therefore, only the principal ones ; and refer,
for farther information, to the 2d and 24th volumes of the
Annales de Chimie , and to Dm Thomson’s memoir in Nichol¬
son’s Journal, vi. 94. Their general qualities are the following :
1. They have a disagreeable taste and smell, resembling the
fumes of burning sulphur.
2. When heated, they emit sulphurous acid and water, and
360
SULPHITES.
CHAP. XII.
then sulphur, which, on the application of an inflamed sub¬
stance, takes fire, and burns violently.
3. Exposed to the atmosphere, in a state of solution, or
moistened with water, they absorb oxygen, and are slowly
converted into sulphates, without undergoing any change in
their state of neutralization.
4. When added to nitric acid, red fumes arise, and the
salts become sulphates. Oxy-muriatic acid produces the same
effect. Concentrated sulphuric acid expels sulphurous acid
gas, which may be collected over mercury.
5. When sulphureted hydrogen gas is passed through a
solution of the sulphites, they combine with an additional
quantity of sulphur, and form sulphureted sulphites. These
compounds are regarded by Gay Lussac, not as sulphites hold¬
ing sulphur in solution, but as resulting from the union of a
base with a distinct acid, to which he has given the name of
the per-sulphurous or hypo-sulphurous acid *, and to its com¬
pounds that of hypo-sulphites . When sulphur is boiled with
the sulphites in solution, sulphur is taken up, and sulphurous
acid escapes f.
6. When perfectly pure, sulphites are not precipitated by
a solution of pure barytes or strontites, or by any of the salts
with base of either of those earths. If a precipitation ensue,
it indicates the presence of a portion of sulphate.
Sulphite of potash crystallizes in the form of lengthened
rhomboidal plates, or of needles, which have sometimes a
slight yellowish tinge. It has a pungent and sulphurous taste,
and is soluble in an equal weight of cold, or in less than an
equal weight of boiling water. At the temperature of 300°
Faht., it loses only about 2 per cent ; but when more strongly
heated, the salt is decomposed, and sustains a loss of about
22 per cent., of which 15 are sulphurous acid, 5 sulphur, and
2 water. When thrown into a red-hot crucible, a blue flame
arises from it, and its weight is diminished in the proportion
which has just been stated. WThen this solution is exposed to
the air, the salt slowly attracts oxygen, and is converted into
* Ann. de Chim. et Phys. vi. 323, note,
f Gay Lussac, 85 Ann. de Chim. 199,
SECT. V.
SULPHITES.
36 1
sulphate of potash. This change goes on more rapidly in
oxygen gas ; or when it is mixed with any substance holding
oxygen in loose combination, as nitric or oxymuriatic acid.
It con tains, in 100 parts, from Dr. Thomson’s experiments,
43.5 acid
54.5 potash
2 water
TOO
Sulphite of soda forms compressed tetrahedral prisms
with dihedral summits. It requires for solution less than its
own weight of boiling water, or four times its weight of cold
water. It effloresces in the air, but much less perfectly than
the sulphate of soda. It is composed, according to Dr. Thom¬
son, of
31 acid
18 soda
51 water
100
Sulphite of ammonia crystallizes in hexahedral prisms
terminated by pyramids with the same number of sides, or in
rhomboidal prisms with trihedral summits. It is soluble in
an equal weight of cold water, or in less than an equal weight
of boiling water. It deliquiates in the atmosphere, and ab¬
sorbing oxygen is changed into sulphate of ammonia, which
becomes dry.
Sulphite of barytes, like the salt formed by uniting the
same base with sulphuric acid, is almost insoluble. When
united with an excess of sulphurous acid, however (which
may be done by dissolving the white powder, that is first
formed, in liquid sulphurous acid), it forms a crystal! izable
salt, still of sparing solubility, consisting of
Base .......... 69.74
Acid . ........ 28.84
Water ........ 1.42
100
362
SULPHURETS.
CHAP. XII.
The solution of this salt may be advantageously used to
purify the solution of any sulphite from sulphuric acid, which
it precipitates in the state of an insoluble sulphate of barytes.
Sulphite of lime is also insoluble, but may be crystal¬
lized by being first dissolved in liquid sulphurous acid. In
this state it requires 800 parts of water for solution.
Sulphite of magnesia differs from the sulphate of this
earth in being vastly less soluble in water, of which it requires
20 parts at the common temperature. Hot water takes up a
farther portion, which is deposited on cooling.
Sulphite of alumine is not crystallizable, but has the
form of a white soft powder, insoluble in water, but soluble
in an excess of acid. It consists, according to Dr. Thomson, of
32 acid
44 alumine
24 water
100
SECTION VI.
Binary Compounds of Sulphur. — 1st, With Alkalies. — 2d, With
Hydrogen.
Art. 1 . — Sulphur ets.
I. The combination of sulphur with tiie fixed alkalies and
earths may be effected by fusing together, in a covered cruci¬
ble, at a degree of heat below redness, equal parts of sulphur
and of the alkali or earth intended to be united with it. The
sulphurets of potash and soda may, also, be obtained by a
similar treatment of six parts of sulphur with eight of either
of the sub-carbonates of those alkalies, previously dried as
completely as possible. The compound may be poured,
while in fusion, upon a smooth stone, and, when cold, pre¬
served in a well closed phial. Its colour is a brownish red or
liver colour, from which property has been derived the gene¬
ric name, formerly in use, of hepar or liver of sulphur .
SECT. VI.
SULPHURETS.
363
It was contended by Van quel in that, during the formation
of sulphurets by fusion, a considerable quantity of sulphur-
eted hydrogen gas is evolved, and that sulphuric acid is also
produced, which, uniting with the alkaline base, composes a
sulphate. It has been shown, however, by Gay Lussac, that
the formation of sulphuric acid takes place only at high tem¬
peratures, and that a sulphuret, which has been prepared
at a degree of heat barely sufficient for the purpose, when
dissolved in water, gives no trace of sulphuric acid, but
abounds with hypo-sulphurous acid . This acid must, how¬
ever have been generated during the act of solution, by the
decomposition of water, for it is incapable of being formed,
or even of existing, at high temperatures.
A pure sulphuret of potash or soda cannot be formed in the
humid way, for the decomposition of the water gives rise to
other products, which, also, exist in the solution. Accord¬
ing to Vauquelin, the sulphuret of lime is an exception to
this rule, aud may be formed by boiling lime and sulphur
with a sufficient quantity of water.
It has been doubted whether, in the production of alka¬
line and earthy sulphurets, the base preserves the state of
an oxide after combination with sulphur, or whether it be
de-oxidized, and thus produce a sulphuret with the metallic
base of the respective alkali or earth. The oxides of the
common metals, it is well known, abandon their oxygen,
when fused with sulphur, and afford true metallic sulphurets.
Gay Lussac has, however, proved that, at a moderate tempe¬
rature, the alkalies unite, as such , with sulphur, and that
compounds are formed which are true sulphureted oxides *.
To prepare sulphuret of ammonia, a mixture of one part
of dry quicklime, one of muriate of ammonia, and half a
part of sulphur, may be distilled from a glass retort by a
gentle heat. The product is a liquid of a brownish yellow
eblour, and an oily consistence, which emits copiously white
and offensive fumes.
Sulphuret of lime, when intended for the purpose of Can¬
ton's phosphorus , is best prepared, by placing in a crucible,
* 6 Ann. de Chim, etPliys. 325,
364*
SULPHUgETS.
CHAP. XII,
alternate strata of calcined and pounded oyster- shells and sul¬
phur; exposing them to a moderate heat; and then confining
them in a bottle with a ground stopper. Or, according to
the original directions of Canton, three parts of oyster-shells,
calcined for an hour and pulverized, are to be mixed with one
of sulphur, and rammed tightly into a crucible, which is to
be kept red-hot for about an hour. The compound, when
cold, lias the properties already assigned to the Bolognian
phosphorus.
II. Sulphurels have the following properties :
(a) In a moist state they emit an offensive smell, and have
a disagreeable taste.
( h ) They change to green the colour of violets, in the same
manner as uncombined alkalies.
(c) They blacken the skin, silk, and other animal sub¬
stances.
(d) They are decomposed by all acids. Into a 'Nooth’s ma¬
chine put a weak solution of sulphuret of alkali, and pass
through it streams of carbonic acid gas. In the course of a
few days, the sulphur will be precipitated, and a carbonate of
alkali will be obtained. This decomposition ensues, instantly,
on adding, to a solution of sulphuret of potash, any of the
stronger acids, as the sulphuric, nitric, or muriatic; and we
obtain a compound of the alkali with the respective acid em¬
ployed.
(e) The solutions of sulphurets absorb oxygen gas, and
abandon part of their sulphur. This may be shown by the
experiments already described (chap, v.) If the change thus
effected be examined, it will be found that the oxygen has
combined with the sulphur, and formed sulphurous acid,
which, uniting with the alkali, has composed the sulphite of
potash. To this sulphite, a portion of the liberated sulphur
unites itself, forming a sulphuret ed sulphite.
(f) If dilute muriatic acid be poured on the solution of
sulphuret of potash or soda, a violent effervescence wall ensue,
and a very offensive gas be disengaged. This gas may be
collected over water. It is termed sulphureted hydrogen gas.
From the experiments of Vauquelin, it appears to be merely
disengaged, and not formed by the action of the acid. The
SECT. VI.
SULPHURETED HYDROGEN.
3 65
following Table shows the composition of a few of the sul-
phurets, as determined by Vauquelin. No sulphuret of mag¬
nesia has yet been proved to exist.
100 Base
Base. Sulphur. take Sulphur.
Sulphuret of Potash .... 47.3 .... 52.7
- - - — Soda . 38. .... 62.
— - — - — - Barytes . . . 65.5 .... 34.5
- — - — Lime. .... 37. .... 63.
111.5
163.
52.5
170.
The quantities of sulphur, which combine with the alkalies
and earths, have been ascertained by the same chemist to be
proportional to the quantities of oxygen, with which their re¬
spective metallic bases are united. But the sulphurets contain
more sulphur than is necessary to form the quantity of sul¬
phuric acid, equivalent to the saturation of their bases.
Art. 2.— Sulphur eted Hydrogen Gas .
This gas may be procured :
1. By the action of diluted sulphuric acid on sulphuret of
iron, prepared in the following manner. A bar of iron is to
be heated to a white or welding heat in a smith’s forge, and5
in this state, is to be rubbed with a roll of sulphur. The me¬
tal and sulphur unite, and form a liquid compound, which
falls down in drops. These soon congeal ; and the compound
must he preserved in a well closed phial.
2. The sulphuret, prepared by melting iron filings with
sulphur in a crucible, does not answer the purpose equally
well, because the gas, which it affords, is mixed with a good
deal of hydrogen gas. So, also, is the sulphureted hydrogen
produced by heating sulphur in hydrogen gas.
3. Gay Lussac prepares sulphuret of iron by introducing
into a matrass two parts by weight of iron filings and one of
flowers of sulphur. To these, water is added in sufficient
quantity to give a thickish consistence ; and the matrass is
heated a little, to favour the combination, which is indicated
by a copious disengagement of heat, and by the whole mass
assuming a black colour. From this compound, sulphuric
acid, diluted with four times its volume of water, separates
sulphureted hydrogen in great abundance. It is better to pre-
4
366
SULPHURETED HYDROGEN.
CHAP. XI r.
pare the compound when wanted, than to keep it ready made,
because, unless very carefully preserved from contact with the
air, it becomes less fit for the purpose of affording gas
4. The sulphuret of potash, if prepared by boiling flowers
of sulphur with liquid potash, quite free from carbonic acid,
gives pure sulphureted hydrogen, when acted upon by diluted
sulphuric or muriatic acid.
II. Its properties are the following:
(a) Its smell is extremely offensive, resembling that of pu¬
trefying eggs.
(b) It is inflammable, and burns either silently or with an
explosion, according as it is previously mixed, or not, with
oxygen gas or atmospheric air. During this combustion,
water results from the union of the hydrogen with the oxygen,
and sulphuric and sulphurous acids from that of the oxygen
and sulphur. Two measures require three of oxygen gas,
one measure of which saturates the hydrogen, and two the
sulphur.
When three parts of sulphureted hydrogen are mingled
with two of nitrous gas, the mixture, on being inflamed, burns
with a yellowish green flame.
(c) It tarnishes silver, mercury, and other polished metals,
and instantly blackens white paint.
(d) It is absorbed by water, which takes up its own bulk,
or according to Saussure twice and a half, or Gay Lussac,
three times, its bulk of the gas ; but in order to obtain so con¬
siderable an absorption, the gas, submitted to experiment,
should be perfectly pure. Water thus saturated acquires the
peculiar smell of the gas. It is this gas which gives to the
Harrogate, and some other natural waters, their disagreeable
odour. Liquid muriatic acid absorbs at least three times its
volume ; and sulphuric acid, diluted with an equal weight of
water, once and a half its volume.
(e) Water, saturated with this gas, reddens the infusion of
violets, in this respect producing the effect of an acid. From
this and other properties, some of the German chemists have
proposed for it the name of hydrothionic acid ; and Gay Lussac
has given it the very objectionable name of hydro-sulphuric
* Ami. de Chim. et Phys. vii. 314.
3
SECT. VI.
SULPHU RETED HYDROGEN.
367
acid , a term which would be much more properly applied to
liquid sulphuric acid.
(f ) W ater impregnated with sulphureted hydrogen, when
exposed to the atmosphere, becomes covered with a pellicle of
sulphur. Sulphur is even deposited when the water is kept in
well-closed bottles.
(g) On the addition of a few drops of nitric or nitrous acid
to the watery solution, sulphur is instantly precipitated. In
this case the oxygen of the acid combines with the hydrogen
of the gas, and the sulphur is separated. The gas itself, also,
is decomposed when transmitted through sulphuric, nitric,
or arsenic acids
(/i) This gas, as will afterwards appear, is decomposed by
mixture with oxy-muriatic acid gas ; and sulphur is precipi¬
tated. Vogel obtained, also, a liquid, analogous to the sul¬
phureted muriatic acid of Dr. Thomson.
(i) It is decomposed also when kept in a state of mixture
with atmospheric air, the oxygen of which combines with
the hydrogen, and forms water, while the sulphur is preci¬
pitated.
(k) A succession of electric explosions throws down sulphur
from it, and the volume of the gas remains unaltered.
(/) When six measures of sulphureted hydrogen gas and
five measures of sulphurous acid gas are mingled together,
the hydrogen of the former unites with the oxygen of the lat¬
ter, and the sulphur of both is precipitated. But five mea¬
sures of sulphurous acid contain twice the oxygen necessary
for saturating six measures of sulphureted hydrogen. Hence
it is probable, that the sulphur is separated in the state of an
oxide.
( m ) It is decomposed when passed over ignited charcoal,
and is converted into carbureted hydrogen gas.
( n ) Sulphureted hydrogen, both in the state of a gas and of
watery impregnation, precipitates all metallic solutions, ex¬
cepting those of iron, nickel, cobalt, manganese, titanium,
and molybdena.
(o) It is copiously absorbed by alkalies, and by all the
earths, excepting alumine and zircon. These alkaline and
earthy combinations are termed hydro-sulphurets.
Journ. of Science, &c. ii, 152.
368
SULPHURETED HYDROGEN,
CHAP. XII*
( p ) When potassium or sodium is made to act on sulphur-
eted hydrogen gas, a brilliant combustion takes place; a
quantity of hydrogen gas is evolved, precisely equivalent to
that which the metal would have separated from water ; the
metal loses its lustre, and becomes greyish, or amber coloured,
or reddish ; and by the action of diluted muriatic acid, the
whole of the sulphureted hydrogen is recovered. This expe¬
riment proves, that sulphureted hydrogen, and consequently
sulphur, contain no oxygen ; for, in that case, the potassium
would not, after being acted on by the gas, evolve the original
quantity of sulphureted hydrogen. All that appears to take
place is, the combination of the metal with sulphur, and the
formation of a sulphuret of potassium or sodium, which dis¬
engages from water exactly as much hydrogen, as would have
been evolved by the metal in its separate state. The results
of Sir H. Davy, which are somewhat different, are satisfacto¬
rily explained by Gay Lussac and Thenard *.
(q) The specific gravity of sulphureted hydrogen gas has
been variously stated. Mr. Kirwan found 100 cubic inches,
at 60° Fahrenheit, and SO inches barometer, to weigh 34.2S6
grains, which makes its specific gravity 1.124. Sir H. Davy
states the weight of the same quantity at S 6.5 grains, and its
specific gravity, therefore, at 1.180. Gay Lussac and The¬
nard determined its specific gravity to be 1.1912 by experi¬
ment, or 1.1768 by calculation; and 100 cubic inches should
weigh 36.33 grains, according to the first of these twro num¬
bers.
(r) Admitting the accuracy of Sir H. Davy’s statement of
its specific gravity, and also that 100 cubic inches of the gas
contain exactly the same volume of hydrogen (= 2.27 grains),
then 36,5 grains of sulphureted hydrogen will contain 2.27
grains of hydrogen ; and 100 grains will consist of
Sulphur .... 93.8
Hydrogen . . 6.2
100.
From these data, winch agree very nearly with those of Ber¬
zelius f, the weight of the atom of sulphur may be stated at
* Recherches, i. 202.
f 81 Ann. de Chiin, 26.
SECT. VI.
HYDRO-SULPHURETS
369
15; for as 6.2 to 93.8 so is 1 to 15 very nearly. The weight
of this atom, therefore, turns out to be the same, whether In*
vestigated by its combinations with oxygen or with hydrogen®
Art. 3, — Hydro- Sulphurets.
In its union with alkaline and earthy bases, sulphureted
hydrogen seems to perform, in a great measure, the functions
of an acid; and presents, therefore, an important exception to
the doctrine of acidification proposed by Lavoisier ; for, in
this instance, a body, which contains no oxygen, possesses
some of the most important characters of an acid, viz. the pro¬
perty of changing vegetable blues to red, and of uniting with
alkalies.
I. The hydro-sulphurets may be formed, by transmitting
sulphureted hydrogen gas, as it issues from the materials that
afford it, through a solution of the alkaline or earthy base.
Or the base, when insoluble, must be kept suspended in water
by mechanical agitation.
II. The hydro-sulphurets have several qualities common to
the whole genus.
1. They are all soluble in water, and the recent solution is
colourless. By exposure to the air, however, it first becomes
green, or greenish yellow, and deposits sulphur on the sides
of the vessel. The glass bottle, containing the solution, be¬
comes black on its inner surface, in consequence of the com¬
bination of sulphur with the oxide of lead contained in the
glass.
2. The solution of hydro-sulphuret of magnesia is decom¬
posed by heat ; that of lime nearly so ; but those of potash
and soda, though rendered much more alkaline by heat, still
contain a large proportion of sulphureted hydrogen.
3. After long exposure to the atmosphere, the solution
entirely loses its colour* and again becomes perfectly limpid.
'When examined, it is found to consist of a combination of
sulphuric acid with the peculiar base of the hydro-sulphuret.
This is owing to the absorption of oxygen, which all hydro-
sulphurets take from the atmosphere ; the formation of a sul¬
phite ; and the conversion of this, by farther oxygenation,
VOL. i, 2 b
370
HYDRO-SULPHURETS.
CHAP. XII.
into a sulphate. Hence, when confined in contact with a
limited quantity of atmospherical air, hydro-sulphurets effect
a diminution of volume ; and may be employed to ascertain
its proportion of oxygen. They entirely absorb pure oxy¬
gen gas.
4. When a hydro-sulphuret, fully charged with gas, is
heated with sulphur, a strong effervescence ensues ; much of
the sulphur is dissolved ; and sulphureted hydrogen escapes.
If the hydro-sulphuret is not fully saturated, sulphur is still
dissolved, but without any escape of sulphureted hydrogen.
5. When an acid is poured on any of the hydro-sulphurets,
the sulphureted hydrogen gas is disengaged and no sulphur is
deposited. This non-precipitation of sulphur distinguishes
hydro-sulphurets, both from sulphurets and hydrogureted sul-
phurets. The acid employed should be one which strongly
retains its oxygen, such as the sulphuric or muriatic ; other¬
wise it will be decomposed. A hydro-sulphuret, wdiich has
been a few days exposed to the air, yields, by this treatment,
sulphurous acid gas, along with sulphureted hydrogen.
6. The solutions of hydro-sulphurets precipitate all metallic
solutions. They also precipitate alumine and zircon from
their solutions, but no other earths.
7. The hydro-sulphurets are, for the most part, susceptible
of a regularly crystallized form.
Hydro-sulphuret of potash forms large transparent
crystals not unlike in size those of sulphate of soda, but having
the shape of four-sided prisms, acuminated with four planes ;
or of six-sided prisms, acuminated by six planes. It is deli¬
quescent, and affords a thick syrupy liquor, which gives a
green colour to the skin. It dissolves readily in water and
alcohol, producing cold. When dilute acids are added to
the solution, a brisk effervescence is excited, but no sulphur
is deposited. Vauquelin found that its solution in water may
be evaporated to dryness, without decomposing the hydro-
sulphuret ; for on heating the residuum, mixed with sulphur,
in a retort, sulphureted hydrogen gas was disengaged abun¬
dantly.
Hydro-sulphuret of soda is a compound, which derives
some importance from its being produced along with carbonate
6
SECT. VI.
SUPER-SULPHURETED HYDROGEN.
371
of soda, in several processes for decomposing the sulphate of
soda #. It is transparent at first, colourless, and crystallized
in four-sided prisms acuminated by four planes. It has an
acrid and alkaline taste, which soon becomes very bitter. Its
solution is colourless, but tinges the skin or paper grefen. It
effervesces briskly with acids, and no sulphur is deposited un¬
less the nitric or oxymuriatic acids are added, which attract
the hydrogen, and throw down sulphur.
Vauquelin has proposed to distinguish these two sulphurets,
which so closely resemble each other, by the following test.
The hydro-sulphuret of potash, when added to a solution of
sulphate of alumine, occasions a crystallization of alum ; but
that of soda has no su<ph action.
Hydro-sulphuret of ammonia may be formed by the
direct mixture of sulphureted hydrogen and ammoniacal
gases in a dry vessel, cooled externally by ice. It is deposited
in needle-shaped crystals. But, for all practical uses, it is
better prepared, by putting a solution of pure ammonia into
the middle vessel of a Nooth’s machine, and passing through
it streams of sulphureted hydrogen gas, till the liquid acquires
a yellowish colour. In this state it constitutes the hepatized
ammonia, so strongly recommended by Dr. Rollo as a remedy
for diabetes.
Hydro-sulphurets of barytes and strqntites are crys¬
tallized salts, having a white silky lustre, and readily soluble
in water f.
Hydro-sulphuret of lime, formed by transmitting sul¬
phureted hydrogen through water, in which lime is kept
mechanically suspended, composes a crystallizable salt, soluble
in water; and having the general properties of hydro-sul¬
phurets J.
Art. 4.— Super -Sulphureted Hydrogen , and Hydrognreted
I. Super-sulphureted hydrogen is obtained, when hydro-sub
* Annales de Chimie, lxiv. 59. t Ibid. Ixii. 181.
t This account differs in some respects from that of V auquelin, Ann, de
Chim. et Phys. vf. 37.
2 B 2
372
SU1PER-SULPHU RETED HYDROGEN.
CHAP. xir.
phuret of potash is poured, by little and little, into muriatic
acid. A very small portion only of gas escapes ; and while
the greater part of the sulphur separates, one portion of it
combines with the sulphureted hydrogen ; assumes the appear¬
ance of an oil ; and is deposited at the bottom of the vesseL
Or, dissolve sulphur in a boiling solution of pure potash ; and
into a phial, containing about its capacity of muriatic acid,
of the specific gravity 1.07, pour about an equal bulk of the
liquid hepar. Cork the phial, and shake it ; the hydrogu-
reted sulphur gradually settles to the bottom in the form of a
brown, viscid, semifluid mass. Its properties are the following :
1 . If gently heated, sulphureted hydrogen gas exhales from
it ; the super-sulphuret loses its fluidity ; and a residue is left,
consisting merely of sulphur.
2. It combines with alkalies and earths ; and forms with
them a class of substances called hydrogureted sulphurets.
3. It is constituted, according to Mr. Dalton, of two atoms
of sulphur, weighing 30, with one atom of hydrogen, and con¬
sists, therefore, per cent, of
Sulphur . .......... 96.75
Hydrogen . ........ 3.25
100.
There are, therefore, three distinct combinations of sulphur
and its compounds with alkalies and earths. The first consist,
simply, of sulphur, united with an alkaline or earthy base,
and are properly called sulphurets. The second are composed
of sulphureted hydrogen, united with a base, and are called
hydro-sulphurets . The third contain super-sulphureted hy¬
drogen, attached to a base, and constitute hydrogureted sul¬
phurets .
The pure sulphurets can exist, as such, only in a dry state;
for the moment they begin to dissolve in water, a decomposition
of that fluid commences; sulphureted hydrogen is formed;
and of this a part is disengaged, while another part, uniting
with an additional proportion of sulphur, composes super-
sulphureted hydrogen. This last, uniting with the base, forms
an hydrogureted sulphuret. At the same time, it has been
SECT. VI.
HYDROGURETED SULPHURETS.
373
slated by Berthollet *, sulphuric acid is composed, by the
action of the sulphur on the oxygen of the water. This how-
ever, Gay Lussac has shown, takes place only when the sul-
phuret has been formed at an unnecessary degree of heat, and
that when carefully prepared at a heat below redness, the so¬
lution of an alkaline sulphuret in water contains sulphurous
and hypo-sulphurous acids, but no sulphuric acid f . The
sulphurets, also, being partly changed, by solution, into hy-
drogureted sulphurets, the effusion of an acid throws down a
quantity of sulphur. A distinguishing character, also, of
solutions of this kind, is that sulphur is precipitated by passing
through them sulphureted hydrogen gas.
According to Proust, if red oxide of mercury be added to
solutions of the kind which have just been described, the sul-
phureted hydrogen is removed, and what remains is a pure
liquid sulphuret, from which acids precipitate sulphur only,
without any effervescence.
II. The hydrogureted sulphurets are also formed by boil¬
ing, along with a sufficient quantity of water, the alkaline, or
earthy base, with flowers of sulphur. Thus a solution of
pure potash, pure soda, or of barytes or strontites, may be
changed into an hydrogureted sulphuret. To prepare this
compound, with base of lime, the powdered earth, mixed
with sulphur, may be boiled with a proper quantity of water,
and the solution filtered or cleared by subsidence. One hun¬
dred grains of lime, or 134 of hydrate, dissolve about 215 of
sulphur, and afford a liquid of 1.146 specific gravity.
The hydrogureted sulphuret of ammonia (which base can^
not, in strictness, owing to its liquid form, compose a true
sulphuret) may be prepared as follows : Mix together, in a
mortar, three parts of hydrate of lime, one part of muriate of
ammonia, and one of flowers of sulphur. Introduce the mix¬
ture into a retort, and apply a receiver. Begin the distilla¬
tion with a gentle heat. The first liquor, that comes over
(long known under the name of Boyle's Fuming Liquor ), has
a light yellow tinge, and emits fumes ; the second has a deeper
* Ann. de Chim. xxv. 239, 269.
f 6 Ann, de Chim. et Phys. 322,
5
374
HYDROGURETED SULPHURETS.
CHAP. XII.
colour, and is not fuming. When the latter begins to ap¬
pear, the fire may be raised.
Another method of forming, by a very simple process, the
hydrogureted sulphurets, consists in digesting, in a gentle
heat, a hydro-sulphuret with powdered sulphur, an additional
portion of which is thus dissolved, while part of the sulphur-
eted hydrogen escapes.
Hydrogureted sulphurets have the following properties :
1. They have a deep greenish yellow colour; an acrid and
intensely bitter taste ; and an excessively offensive smell.
2. They deposit sulphur when kept in close vessels ; become
much more transparent and lighter coloured ; and less offen¬
sive to the smell.
3. They rapidly absorb oxygen from the atmosphere, and
from oxygen gas. Hence their employment in eudiometry *.
4. On the addition of dilute sulphuric, or muriatic, or of
certain other acids, they are decomposed. Sulphureted hy¬
drogen gas is evolved, and sulphur is precipitated.
5. When boiled in contact with filings of silver or of cop¬
per, and of those metals only, Vauquelin found that they lose
their excess of sulphur, and become simple hydro- sulphurets.
Hydrogureted sulphurets of potash and of soda dif¬
fer very little from each other. They may be formed by boil¬
ing solutions of pure potash or soda with flowers of sulphur.
When very concentrated, they have a deep reddish brown
colour, a nauseous taste, a disagreeable odour, and a soapy
feel, tinging the cuticle black. When exposed to the air, a
thin pellicle of sulphur forms upon their solutions, which, by
sufficiently long exposure, are changed into sulphates. When
an acid is suddenly added, sulphur is thrown down, which
becomes, when washed with sufficient water and dried, almost
white, and constitutes what has been called precipitated sul¬
phur, milk of sulphur, or magistery of sulphur.
Hydrogureted sulphuret of ammonia may be formed
by the process already described, or by digesting hydro-sul¬
phuret of ammonia with sulphur, a portion of which is dissolved.
Hydrogureted sulphuret of barytes is obtained by
* See chap, v. sect. 4.
SECT. VI.
3ULPHURET OF CARBON.
315
boiling crystals of pure barytes with one fourth their weight of
sulphur and sufficient water. Two compounds are formed,
viz. an hydrogureted sulphuret, which has a red colour and
remains in solution ; and colourless crystals, which are sup¬
posed to be a hydro-sulphuret of barytes. Strontites forms
similar compounds.
Hydrogureted sulphuret of lime is formed by boiling
hydrate of lime with a third its weight of sulphur and ten
times its weight of water. The compound has a deep orange
colour, and is of importance from its application to eudiome-
trical purposes. From the experiments of Vauquelin, it ap¬
pears probable, that the proportion of its ingredients varies,
and is attended with corresponding differences of solubility
and other properties #.
Sulphuret of Carbon , or Alcohol of Sulphur ,
There has been much controversy respecting the nature of
this compound; and several contradictory statements have
been given of its composition. It was discovered by Lampa-
dius in 1 79 6, and was considered by him as consisting of sul¬
phur and hydrogen. Clement and Desormes were led, by
their researches, to deny the presence of the latter element ;
and to conclude that it is a compound of sulphur and charcoal.
This inference was afterwards controverted by Vauquelin and
by Berthollet, jun. ; and the experiments of Cluzel also were
supposed by their author to be favourable to the opinion, that it
contains hydrogen f . In a report, however, on the Memoir
of Cluzel, MM. Berthollet, sen. Thenard, and Vauquelin de¬
scribe experiments made by the last-mentioned chemist, which
lead them to believe that the alcohol of sulphur is a true binary
compound of sulphur and charcoal only % ; and this inference
has been proved to be correct, by the recent and able investi¬
gations of Drs. Berzelius and Marcet§.
To prepare this substance, a coated earthen tube, of about
one inch and a half in diameter, partly filled with small pieces
of charcoal, may be disposed in a furnace as represented fig.
40, cc, one end being placed higher than the other. To this
* Ann. deChim. et Phys. vi. 39. t Ann. de Chim. lxxxiv. 73
\ Ann. de Chim. Ixxxiii. 252. § Phil Trans. 1813.
376
SULPHURET OF CARBON.
CHAP. XII.
end may be adapted a glass tube, open at both ends, contain¬
ing small bits of sulphur ; and, to the other end, by means of
an adopter, is to be fixed a curved tube, passed into water
contained in a two- necked bottle. The part of the tube, con¬
taining the charcoal, may then be made red-hot ; and, when
this happens, the bits of sulphur are to be pushed forwards,
one by one, by means of a wire, carefully excluding air. As
soon as the sulphur comes into contact with the charcoal,
bubbles of gas will be produced in great abundance, and a va¬
pour will appear, which will condense, under the water in the
bottle, into a liquid, of which, in the course of a day, about
half a pint may be procured. This liquid may be purified by
redistilling it at a very gentle heat, not exceeding 100° or 110°
Fahrenheit; and some dry muriate of lime may be put into
the retort, in order to obtain the fluid perfectly free from
water. The liquid which comes over is quite pure, and some
sulphur remains in the retort.
The alcohol of sulphur has the following properties :
1. It is eminently transparent, and perfectly colourless.
Sometimes, immediately after distillation, the oily liquid ap¬
pears a little opaque and milky ; but the next day it is found
to have become completely limpid. It has an acrid, pungent,
and somewhat aromatic taste ; its smell is nauseous and fetid,
though differing from that of sulphureted hydrogen.
2. Its specific gravity is 1.272: its refractive power, as
ascertained by Dr. Wollaston, is 1.64-5. Its expansive force
(at 30 inches barometer, and 53±° Fahrenheit) is equal to the
pressure of 7.36 inches of mercury ; so that air, to which it is
admitted, will dilate about one fourth of its volume. It boils
briskly under the common atmospheric pressure, at a tempe¬
rature of 1 05° or 110° Fahrenheit. It does not congeal,, at a
temperature as low as 60° below 0 of Fahrenheit.
3. It is highly inflammable, and takes fire at a temperature
scarcely exceeding that at which mercury boils. Its flame is
bluish, and it emits copious fumes of sulphurous acid. If a
long glass tube, open at both ends, be held over the flame,
care being taken to keep the tube quite cool, no moisture what¬
ever is deposited on its inner surface, a sufficient proof of the
absence of hydrogem
SECT. VI.
SULPHURET OF CARBON.
377
4. The oily liquid readily dissolves in alcohol and ether,
though not in all proportions, and these solutions are decom¬
posed by the addition of water. It readily incorporates with
fixed and volatile oils, and rapidly dissolves camphor. It is
not soluble in water.
5. In its liquid state, it suffers no change on being heated
with potassium; but potassium, when heated in its vapour, be¬
comes ignited, and emits a reddish flame. The residue, when
washed with wrater, affords sulphuret of potash and charcoal.
6. It does not tarnish mercury or its amalgams, nor silver,
unless it contain more sulphur than is essential to its consti¬
tution.
7. The alkalies dissolve it entirely, but very slowly. Of
the acids, none exert any sensible action on it, but the nitro-
muriatic and liquid oxymuriatic acids, which occasion its de¬
composition.
8. When transmitted over ignited copper or iron turnings,
alcohol of sulphur is decomposed, the metal combining both
with charcoal and sulphur ; and a rose coloured fluid is ob¬
tained, differing in its sensible qualities from the original
liquid, and apparently consisting of the same elements in dif¬
ferent proportions.
The proportions of the elements of sulphuret of carbon are
deduced by Berthollet, Thenard, and Vauquelin, to be from
14 to 15 parts of charcoal, and from 85 to 86 of sulphur, in
100. This statement of its composition nearly agrees writb
that inferred by Drs. Berzelius and Marcet ; viz.
Sulphur........ 84.83 ..or .. 100.
Carbon . . 15.17 ........ 17.89
100. 117.89
The above-mentioned numbers establish the proportion of
the elements of this compound to be two atoms of sulphur to
one of carbon.
The sulphuret of carbon was found by Berzelius to be capa¬
ble of uniting with alkaline and earthy bases, and of forming
compounds which may be called Carbo-Sulphurets. But their
properties, and the proportion of their elements, require fur¬
ther investigation.
378
SULPHURET OF CARBON.
CHAP. XII.
In a subsequent memoir in the same volume of the Philoso¬
phical Transactions, Dr. Marcet describes the extraordinary
power of alcohol of sulphur, in producing cold. The bulb of
a thermometer being covered with fine lint, and moistened
with a few drops of the liquor, the mercury sinks rapidly from
60° to 0, and under the exhausted receiver of an air-pump,
from + 70°, to 70° or even 80° below 0, so that by this pro¬
cess mercury may readily be frozen.
379
CHAPTER XIII.
COMBINATION OF NITROGEN WITH OXYGEN, CONSTITUTING
NITRIC ACID, — NITROUS GAS, — NITROUS OXIDE, — AND COM¬
POUNDS OF NITRIC ACID WITH ALKALIES.
W HEN nitrogen and oxygen gases are mingled together,
in whatsoever proportions they are employed, no combination
ensues. The result is a simple mixture of the two gases,
which do not, like inelastic fluids, separate on standing, but
remain diffused through each other for an indefinite length of
time. This is the case with the air of our atmosphere; and
it is fortunate that such a provision of nature exists, since the
atmosphere contains the elements of several combinations
which, if actually formed, would be fatal to animal and vege¬
table life. When, however, either one or both of these ele¬
ments is in a condensed state, or deprived of part of that
caloric which keeps the particles of all gases at a distance
from each other, they unite and form compounds, distin¬
guished by very striking properties. According to the pro¬
portions in which the oxygen and nitrogen exist in these
compounds,' their qualities undergo a remarkable variation,
so that from two elementary bodies, variously united, we have
several compounds, totally unlike each other in external qua¬
lities, as well as in their chemical relations.
Before describing the compounds of oxygen and nitrogen
individually, it will contribute to perspicuity to take a general
survey of the whole. Some of them exist essentiafly in an
aeriform state, and are capable of uniting with water and
other liquids in only small proportions. Others, again, com¬
bine with water to such an extent, that the liquid form is the
only one under which they occur to our observation. When
entirely deprived of water, they are all essentially gaseous
bodies.
In a series of the compounds of nitrogen, founded on their
proportion of oxygen, they occupy (excluding atmospherical
air from the number) the following order, the last containing
380
NITROGEN WITH OXYGEN.
CHAP. XIII
the largest proportion of oxygen— nitrous oxide — nitric oxide
or nitrous gas— per-nitrous acid — nitrous acid or nitrous vapour
— and nitric acid. The two first are sparingly soluble in
water ; but the three last unite with it largely, and form liquid
compounds of decidedly acid taste and quality. *
The following Table exhibits the composition of three of
these bodies, the calculation being founded on the experiments
of Sir H. Davy, published in the year 1800 in his <fi Re¬
searches.” Oxygen gas is assumed to weigh 33.8 grains, and
nitrogen, 29.5 for 100 cubical inches.
Proportion of Proportion by
Elements by Weight. Measure.
Nitrous
oxide . . ,
r~ — /s~
Nitrogen.
)
Oxygen.
36.70 . .
r~ ^
Nitrn. gas.
)
Ox. gas.
50.63
eras . .
. 44.0^
55.95
.... TOO.
110.
208.60
Nitrous
••••••
acid * . . .
70.50 ..
.... 100.
From a comparison of the third and fourth columns of the
foregoing Table, it is obvious, that in nitrous oxide, the ni¬
trogen is, in volume, very nearly double the oxygen ; that in
nitrous gas, the two elements exist in almost equal volumes ;
and that in nitrous acid, the oxygen is a little more than twice
the volume of the nitrogen. These coincidences, and others
of the same kind, are the foundation of the theory advanced
by Gay Lussac; viz. that compounds , whose elements are
gaseous , are constituted either of equal volumes of those elements ;
or , that if one of the elements exceeds the other , the excess is by
some simple multiple of its volume. That the proportions of
nitrogen and oxygen by measure do not, in the foregoing in¬
stances, exactly conform to this law, is ascribed by Gay Lus¬
sac to unavoidable inaccuracies, attendant on all delicate pro¬
cesses for determining the constitution of gaseous bodies. In
one instance, this was proved experimentally ; for M. Retard,
by the combustion of potassium in 100 measures of nitrous
gas, obtained exactly 50 measures of nitrogen. Hence the
table, corrected to coincide with the views of Gay Lussac,
* These were at first stated to be the proportions of the elements of nitric
acid but they apply more correctly to nitrous acid.
CHAP. XIII.
NITROGEN WITH OXYGEN.
381
and enlarged so as to comprehend all the known compounds
of nitrogen, will stand as follows :
Measures of 100 grains contain
rr - A ~~ — i r-~^- — —y
Nitrogen. Oxygen. Nitrogen. Oxygen.
Nitrous oxide consists of . . 100 50.... 63.58 36.42
. . gas . ..100 100 - 46.60 53,40
Per-nitrous acid . 100 150..,. 42.02 57.98
Nitrous acid . . 100 200 .... 30.40 69.60
Nitric acid . . 100 250.... 25.97 74.03
Supposing the foregoing proportions by volume to be cor¬
rect, the proportions by weight will be as follows :
In weight of
Nitrogen. Oxygen,
Nitrous oxide consists of . 100 -f 57
■ - ■ ■ gas . 100 + 114
Per-nitrous acid . 100 + 171
Nitrous acid . . 100 + 228
Nitric acid . . 100 + 285
In all these compounds, the elements are in a state of con¬
densation, except in nitrous gas, in which the nitrogen and
oxygen, according to Gay Lussac, are precisely in the same
state of density, as in nitrogen and oxygen gases. In the
other compounds, the contraction, he apprehends, is exactly
equivalent to the bulk of the oxygen gas. For example, in
100 measures of nitrous oxide, consisting of 100 measures of
nitrogen gas and 50 measures of oxygen gas, the condensa¬
tion is 50 measures. On the same principle 100 measures of
nitrogen gas and 200 of oxygen gas constitute 100 of nitrous
acid gas ; and 100 measures of nitrogen and 250 of oxygen
compose 100 of gaseous nitric acid.
Mr. Dalton, in his “ New System of Chemical Philosophy,”
has given a Table of the Compounds of nitrogen and oxygen,
which differs essentially from that of Gay Lussac. This table,
however, it is unnecessary to copy, because it has been since
materially altered by the author, who has presented it under
the following corrected form *,
* Thomson’s Annals, ix. 193.
3 82
NITROGEN WITH OXYGEN.
CHAP. XIII.
Volumes of
- A - 'v
Nitrogen. Oxygen.
Nitrous oxide ... 100 + 62
— - gas _ 100 + 124
Pernitrous acid . . 100 + 186
Nitrous acid ... . 100 + 248
Nitric acid .... 100 + 810
Atoms of Symbol *.
( - A — -
Nitrogen. Oxygen.
2+1 (BCXD
1 + i QO
2 + 3 (3010
1 + 2 OCDO
2 + 5
It will be obvious, from a comparison of this table with the
foregoing one, that it assigns to all the compounds of nitrogen,
24 per cent, or very nearly one fourth, more oxygen, than is
stated by Gay Lussac to enter into their composition. It is
admitted, on all hands, that setting out from nitrous oxide,
the other compounds of nitrogen contain proportions of oxy¬
gen, which are simple multiples, both in weight and in volume,
of that existing in nitrous oxide. The question, which is still
disputed by the opponents of the theory of volumes, is whether
it be true that one volume of nitrogen unites with either ex¬
actly half a volume of oxygen, or with exactly an equal
volume, or a double volume, and so on. Analogy is certainly
in favour of this opinion ; for the instances are numerous, in
which gaseous bodies observe the law respecting volumes, de¬
duced by Gay Lussac ; and we have net, at present, any well
ascertained exception to it. The argument, which, perhaps,
weighs most in its favour, when applied to the combinations
of nitrogen and oxygen, is that, assuming nitrous oxide to
consist of one volume of nitrogen and half a volume of oxy¬
gen, and multiplying the oxygen of nitrous oxide by 5, we
are led to proportions constituting nitric acid, which almost
exactly agree with those deduced by Dr. Wollaston from the
experiments of Richter and Phillips.
If it should, hereafter, be unquestionably established that
the elements of the compounds of nitrogen and oxygen are
truly expressed by the table of Gay Lussac, it will then fol¬
low that the number representing the atom of nitrogen (oxy-
* O representing oxygen, and 0 nitrogen,
SECT. I.
NITRIC ACID.
383
gen being taken at 7.5) must be 13, or (oyxgen being 10)
17.5. In this determination, it is taken for granted that the
two elements exist atom to atom in nitrous oxide, and that
this, and not nitrous gas, is the true binary compound. But
if, with Mr. Dalton, we suppose nitrous oxide to be consti¬
tuted of two atoms of nitrogen to one of oxygen, we must
then express the weight of the atom of nitrogen, either by
13 -r- 2 = 6.5, or, taking oxygen at 10, by 17.5 *4- 2 = 8.75.
It appears to me, however, most probable, that the former
view is the correct one, and that
Nitrous oxide consists of 1 atom of nitrogen + I of oxygen.
Nitrous gas . . . .
....... +2
Per-nitrous acid ....
....... +3
Nitrous acid .......
. . . . 1 .......
....... T 4
Nitric acid .........
It is obvious that as the five compounds of nitrogen and
oxygen, which have been already described, contain the same
elements, and differ only in their proportion, they may be
converted into each other, by adding or subtracting a due
proportion of oxygen. Thus nitric acid, by contact with
some of the oxidizable metals, is converted into nitrous gas ;
and nitrous gas, by abstracting a farther quantity of oxygen,
is changed into nitrous oxide. Again, by adding oxygen to
nitrous gas, it may be reconverted into per-nitrous, nitrous,
or nitric acid, according to the proportion of oxygen which
is added, and the circumstances under which the combination
is effected.
SECTION I.
Nitric Acid .
I. The direct combination of nitrogen and oxygen, afford¬
ing a decisive synthetic proof of the nature of this acid, may
be effected by passing electric sparks through a mixture of
nitrogen and oxygen gases. The experiment is an extremely
laborious one, and requires, for its performance, a powerful
3S4
NITRIC ACID.
CHAP, Xllx„
electrical machine ; but those who are disposed to repeat it,
may proceed as follows :
Let the tube, fig. 84 c, be filled with, and inverted in, mer¬
cury. Pass into it a portion of atmospherical air, or an arti¬
ficial mixture of nitrogen and oxygen gases, in the proportion
of one of the former to two of the latter. — Let an iron wire,
lengthened out with one of platinum, be introduced within
the tube, so that the latter metal only may be in contact with
the mixed gases ; and let the end of this wire be distant about
one fourth of an inch from the extremity of the upper con¬
ducting one. When the apparatus is thus disposed, pass a
series of electric sparks or shocks through the gases for several
hours. The mixture will be diminished in bulk; will redden
litmus-paper when enclosed in it ; and will exhibit distinctly
the smell of nitrous acid. If the experiment be repeated,
with the addition of a few drops of solution of potash, in con¬
tact with the gases, we shall obtain a combination of nitric
acid with potash.
This interesting experiment on the generation of nitric acid
we owe to Mr. Cavendish, who discovered the fact in the
year 1785*. The proportions, which he found to be neces¬
sary for mutual saturation, were five parts of oxygen gas and
three of common air, or seven parts of oxygen gas to three of
nitrogen gas. The acid, thus obtained, being constituted of
100 measures of nitrogen + 233 oxygen, appears therefore to
have been intermediate between nitrous and nitric acid, or
more probably consisted of both those acids in a state of mix¬
ture. No evolution either of light or heat attends this com¬
bination, which is very slowly and gradually effected.
Another synthetic proof of the production of nitric acid
will be stated under the article nitrous gas. It is furnished by
the generation of nitrous gas, and ultimately of nitric acid,
when ammonia is brought into contact with the black oxide
of manganese.
For all purposes of utility or experiment, however, nitric
acid is prepared in a different manner, viz. by the decompo-
* Philosophical Transactions, Ixxv.
SECT. I.
NITRIC ACID.
385
sition of nitrate of potash, in a way which will be described
in the section on that salt.
II. The analysis of the nitric acid may be obtained by
driving its vapour through a red-hot porcelain tube (fig. 40,
c c), and receiving the generated gases, which prove to be a
mixture of nitrous acid, oxygen, and nitrogen gases.
III. The liquid nitric acid has the following properties :
(a) It is heavier than water, in the proportion of 1.5 or
upwards to 1. Proust obtained it as high as 1.62; and the
specific gravity of real nitric acid, which cannot, however, be
obtained separately, may be calculated at 1.75. In its heaviest
form, it still contains a portion of water, which is essential to
its existence in a liquid state, and without which its elements
would separate from each other. In acid of the sp. gr. 1.50,
the water amounts, calculating from the data furnished by Dr.
Wollaston, to 25.11 grains in 100 grains of acid; or accord¬
ing to Mr. R. Phillips to 25.09.
Pure nitric acid may be considered as a gaseous body, of
the specific gravity, compared with common air, of 2440 :
one hundred cubic inches, at 55° Fahrenheit and under 30
inches pressure, weigh, according to Sir H. Davy, 76 grains ;
or corrected to the temperature of 60° Fahrenheit, they weigh
75.21 grains. The liquid acid (termed by Davy hydro-nitric
acid) consists of this gas condensed by water, of which it con¬
tains various proportions. We have not, however, at present,
documents sufficient for the construction of an accurate Table
of the quantities of real nitric acid in acids of different den¬
sities. According to Sir H. Davy, the strongest acid (sp. gr.
1.55) contains 14.4 parts of water in 100 ; and acid of sp. gr.
1.42 contains 25.2 of water in 100 The Table published
by Mr. Dalton f that philosopher has since found reason to
believe to be inaccurate; but the following results, which he
has been so good as to communicate to me, he thinks are en-
O
titled to greater confidence.
* Elements, p. 265.
f New System, p. 355.
386
NITRIC ACID.
CHAP. XIII.
Table of the quantity of real Acid in Nitric Acid of different
densities.
Parts of
Acid.
Parts of
Water.
Acid per ct.
by weight.
Acid per ct.
by measure.
Specific
Gravity.
45
+
8
84.9
137.5?
1.62?
45
4*
16
73.8
114.4?
1.55?
45
+
24
65.2
96.4
1.48 +
45
+
32
58.4
84.
1.44
45
+
40
53.
74.7
1.41
45
+
48
48.4
67.2
1.39
45
+
56
44.5
60.5
1.36
45
+
64
41.3
55.3
1.34
45
+
180
20.
22.8
1.142
The Table of Mr. Dalton, Dr. Ure believes, however, to
be deficient in accuracy, and he has constructed two others
(for which see the Appendix), the first from experiments on
the mixture of nitric acid of specific gravity 1.500 with water,
in the proportions of 95 + 5, 90 + 10, 80 -f- 20, &c; and
the second from the calculation of the intermediate terms by
a law of progression, which may be thus stated : The specific
gravity of dilute acid, containing 10 parts in the hundred of
acid of density 1.500, is by experiment 1.054. Taking this
number as the root, its successive powers will give us the
successive densities, at the terms of 20, 30, 40 per cent. &c.
Thus 1054 2 = 1.111 is the specific gravity corresponding to
20 strong acid + 80 water; 10543 = 1.234 the density of 30
strong acid -f 70 water; and hence any one term being given
the whole series may be found.
(b) Pure gaseous nitric acid, according to the experiments
of Sir H. Davy, published in the year 1800, is composed in
100 grains, of 294 azote, and 70^-oxgen. This approximation
differs but little from the proportions deducible from the syn¬
thetic experiments of Cavendish, viz. 27.8 nitrogen to 72.2
oxygen. The later results of Sir H. Davy have led him, how¬
ever, to believe, that 4 in volume of nitrous gas and 2 of
oxygen gas, when condensed in water, absorb 1 in volume of
oxygen to become nitric acid. Now, estimating the oxygen
gas, existing in nitrous gas, at one half its volume, and taking
SECT. I.
NITRIC ACID.
38?
the specific gravities of oxygen and nitrogen gases at the num¬
bers already given, 100 parts by weight of nitric acid will
consist of
4
Oxygen ..... - ..... 74.13 ........ 286
Nitrogen. ... - - - 25.8 7 . .,100
100 286
In investigating what number should be used as the equi¬
valent of nitric acid, Dr. Wollaston was led to inquire into
the composition of that acid ; and, from his own experiments,
and those of Richter and Phillips, he infers the oxygen, which
nitric acid contains, to be by weight to the nitrogen, as 50
to 17.54. Hence nitric acid, as it exists in nitre, will be
composed, by weight of
Oxygen . . 74.03 ...... 100 _ ..285
Nitrogen ........ 25.97 ...... 35 . 100
100. 135 385
By an easy calculation, it will be found that the nitrogen,
in 100 grains of nitric acid thus constituted, is equal in vo¬
lume to 88 cubic inches, and the oxygen to 219. But as 88
to 219, so is 100 to 249; and on this view of the nitric acid,
it is composed of 1 volume of nitrogen and 2\ of oxygen,
which agrees with the result of Sir H. Davy, and with the
latest determination of Gay Lussac *. These proportions ap¬
pear on first view to be favourable to the opinion, that nitric
acid consists of two atoms of oxygen to one of nitrogen ; for
as 75 to 25, so is 15 (twice 7.5) to 5, the number already de¬
duced from the analysis of ammonia, as representing the
weight of the atom of nitrogen. It must be acknowledged,
that there is some uncertainty respecting the weight of the
atom of that element. Dr. Wollaston deduces its equivalent
(oxygen being 10) to be 17.54 ; and hence the atom of nitro¬
gen will bear to that of oxygen the proportion of 13.15 to
7.5 ; and nitric acid, according to this view, will consist of
5 atoms of oxygen = 37.5, and 1 atom of nitrogen = 13.15;
* Ana. de Chim. et Phys. i. 404
2c 2
388
NITRIC ACID,
CHAP. XIII,
and its atom will weigh 50.20. Farther investigation must
determine, which of these views is most conformable to
truth.
(c) Hydro-nitric acid is perfectly limpid and colourless, and
emits white fumes, when exposed to the air.
( d ) It gives a yellow stain to the skin.
(< e ) It boils at 248° Fahrenheit, and may be distilled over,
without any essential change. This, however, is true only of
acid of the specific gravity 1 .42 ; for an acid, weaker than this,
is strengthened by being boiled ; while an acid, stronger than
1.42, becomes weaker by boiling. All the varieties of nitric
acid, therefore, are brought, by sufficient boiling, to the spe¬
cific gravity 1.42.
(f) Hydro-nitric acid may be frozen by the application of
a sufficiently low temperature. Like sulphuric acid, there is
a certain point of density, at which it most readily congeals.
Mr. Cavendish has described this, not by its specific gravity,
but by the quantity of marble which it is capable of dissolv¬
ing. When it takes up -^^-ths of its weight, in which case
its specific gravity is 1.3, the acid freezes at 2° below 0 Fah¬
renheit. When considerably stronger and capable of dissolv¬
ing -j^-i-ths, it required cooling to — 41.6,* and when so
much diluted as to take up only it did not congeal
till cooled to — 40.3 *.
(g) Strong hydro-nitric acid absorbs moisture from the at¬
mosphere; in consequence of which it increases in weight,
and diminishes in specific gravity.
(h) When two parts of the acid are suddenly diluted with
one of water, an elevation of temperature is produced to about
112° Fahrenheit; and the admixture of 58 parts by weight of
acid of specific gravity 1.50 with 42 parts of water, both at
60° Fahrenheit, gives a temperature of 140° f. When more
water is added to this diluted acid, its temperature is reduced.
Snow or ice added to the cold dilute acid is instantly liquefied,
and an intense degree of cold is produced.
(i) It becomes coloured by exposure to the sun’s light, pass-
* Phil. Trans. 1788.
+ Dr, Ure, Journ. of Science, iv. 298.
SECT. I.
NITRIC ACID,
389
ing first to a straw colour, and then to a deep orange. This
effect is produced by the union of the light of the sun with
oxygen, in consequence of which the proportion of the acidi¬
fying principle to the nitrogen is diminished.
By exposing it to the sun’s rays in a gas bottle, the bent
tube of which terminates under water, oxygen gas may be
procured.
(k) This acid retains its oxygen with but little force. — Hence
it is decomposed by ail combustible bodies, which are oxy¬
genized by it, with more or less rapidity in proportion to their
affinity for oxygen.
1. When brought into contact with hydrogen gas at a high
temperature, by transmitting them through an ignited porce¬
lain tube, a violent detonation ensues. This experiment,
therefore, requires great caution. 2. Poured on perfectly dry
and powdered charcoal, it excites the combustion of the char¬
coal, which becomes red-hot, and emits an immense quantity
of fumes. 3. It also inflames essential oils (as those of tur¬
pentine and cloves), when suddenly poured on them. In
these experiments, the acid should be poured out of a bottle,
tied to the end of a long stick ; otherwise the operator’s face
and eyes may be severely injured. 4. Nitric acid is decom¬
posed, by boiling it in contact with sulphur, which attracts
the oxygen, and forms sulphuric acid.
(l) The hydro-nitric acid is also decomposed by metals;
as iron, tin, zinc, copper, &c., and with different phenomena,
according to the affinity of each metal for oxygen. This may
be seen, by pouring some strong nitric acid on iron filings, or
powdered tin. The acid must be of greater density than
1.48, otherwise it will not produce the effect. Violent heat,
attended with red fumes, will be produced, and the metals will
be oxydized.
(m) If the action of metals on nitric acid be more mode¬
rately conducted, a new product is obtained in a gaseous state.
Dilute some nitric acid of commerce with 6 or 8 parts of
water, and dissolve, in this, some turnings of copper, or a
portion of quicksilver, applying a gentle heat. — This must be
done in a gas bottle, and the product, received over water, is
nitrous gas, or nitric oxide. Mr. Dalton recommends acid,
S90
NITROUS GAS.
CHAP. XIII.
of density 1.2 or 1.3, to be poured on filings of copper, with¬
out any other heat than that which the action of the acid
and metal on each other occasions.
SECTION II.
Nitrous Gas, or Nitric Oxide.
The properties of this gas, procured in the manner de¬
scribed at the close of the last section, are the following :
(a) It is permanent over water ; but it is absorbed in the
proportion of about 1 volume to 18 or 20 water, when agi¬
tated with water which has been recently boiled, and has be¬
come cold. This solution, according to La Grange *, is con¬
verted, by long keeping, into nitrate of ammonia, in conse¬
quence of the decomposition of the water.
Nitrous gas is rather heavier than common air. One hun¬
dred cubic inches at 55°, barometer 30°, were stated by Sir
H. Davy in 1800, to weigh 34.26, or at 60° Fahrenheit 33.80
grains. He now, however, gives the weight of 100 cubic
inches at 32 grains, and hence its specific gravity is 1.050.
Berard’s determination is considerably lower; viz. 1.0388 by
experiment, or 1.0364 corrected by calculation.
(b) When well washed with water, it is not acid. It will
be found not to redden the colour of litmus. This may be
shown by introducing a piece of paper, tinged with that sub¬
stance, into ajar of nitrous gas, standing inverted over water.
To accomplish this, the paper should be fastened to the end
of a glass rod or a piece of stick. The colour will remain
unchanged.
(e) It extinguishes flame, and is fatal to animals. Hom-
berg’s pyrophorus, however, is inflamed by it ; and charcoal
and phosphorus, introduced into it when in a state of actual
combustion, continue to burn vehemently.
(d) Mingled with hydrogen gas, it imparts a green colour
to its flame. It does not, however, explode with hydrogen in
* Vol. i. p. 131.
SECT. II.
NITROUS GAS.
391
any proportion, nor with any of the varieties of carburetted
hydrogen. But, when mixed with ammonia, an electric
spark produces a detonation, as I have shown in the Philo¬
sophical Transactions for 1809. The proportions required for
mutual saturation are about 120 measures of nitrous gas to 100
of ammonia.
(e) When mixed with oxygen gas, red fumes arise; heat is
evolved; a diminution takes place ; and if the two gases be in
proper proportion, and perfectly pure, they disappear entirely.
Ten measures of oxygen, Mr. Dalton asserts, may be made
to condense any quantity of nitrous gas, between 13 and 36
measures, accordingly as the mixture is conducted ; and Gay
Lussac finds that 100 measures of oxygen gas condense over
water from 134- to 365 nitrous, but in a dry glass vessel only
204, which, allowing for inaccuracies, may be stated at 200.
In the latter case the total 300 measures become 200 of nitrous
acid vapour.
(f) The same appearances ensue, less remarkably, with
atmospheric air; and the diminution is proportionate to the
quantity of oxygen gas which it contains. On this property,
of its condensing oxygen, but no other gas, is founded the
application of nitrous gas to the purpose of eudiometry9 or of
ascertaining the purity of air. The sources of error, in its
employment in this mode, have hitherto been considered such
as to forbid our relying implicitly on the results which it may
afford. Learning, however, from Mr. Dalton, that he con¬
stantly employs nitrous gas in determining the purity of air,
and with perfect satisfaction as to the accuracy of his results,
I have obtained from him the following communication. It
may be necessary to premise, that for applying nitrous gas to
this purpose, two tubes will be found convenient, shaped like
fig. 24 ; each from three to four tenths of an inch in diameter;
eight or nine inches long, exclusive of the funnel-shaped part;
and accurately graduated into minute aliquot parts. What
these parts are, is of no consequence. Hundredth parts of a
cubical inch give rather too large divisions of the scale; but
if each of these be divided into two, the scale will be suffi¬
ciently small. If the tube employed be not long enough to
comprise 100 of these parts* the experiment may be made on
6
3 92
NITROUS GAS.
CHAP. XIII.
50 parts only of atmospherical air ; and the results, multiplied
by 2, will give the proportion in 100 parts.
44 To use nitrous gas accurately in eudiometry, it is only
44 requisite to take both gases in a dilute state, namely, con-
44 taining four or five times their bulk of azotic gas (which
44 atmospheric air naturally does), or of any other gas not
44 acted upon by nitrous or oxygen gases. In this case, if an
44 excess of one gas be used, the other is, in a few minutes, en-
44 tirely taken up, and in a constant proportion ; whatsoever
44 may be the form of the vessel, or the manner of mixing the
44 gases. The proportion is 1 of oxygen to 1.7 of nitrous, so
44 that 10-27ths of the diminution over water are oxygen, and
44 17-27ths nitrous gas. It is proper, as soon as the greater
part of the diminution has ensued, to transfer the mixture
44 through water into a graduated vessel, without using any
44 agitation.
44 If pure nitrous gas be admitted to pure oxygen gas in a
44 narrow eudiometer tube, so that the oxygen gas is upper-
44 most, the twro unite very nearly in the same uniform pro-
44 portion as above. If, on the other hand, the nitrous be
44 the upper gas, a much less quantity of it disappears, viz.
44 1.24 nitrous to one oxygen. If undiluted nitrous gas be
(i admitted to pure oxygen gas in a whde vessel over water, the
44 whole effect takes place immediately ; and one measure of
44 oxygen will condense 3.4 nitrous gas.
44 To render this rule more intelligible, an example may
44 be necessary. Let 100 measures of common air be admitted
*4 to 100 measures of a mixture of nitrous gas, with an equal
44 volume of azotic or hydrogen gas. After standing a few
44 minutes in the eudiometer, there will be found 144 measures.
44 The loss 56 being divided by the common divisor, 2.7, gives
44 21 nearly for the oxygen gas present in 100 measures of
14 common air.”
To these directions I may add, that when atmospherical air
is the subject of experiment, it is scarcely necessary to dilute
the nitrous gas, with any other gas, previously to its use. If
a number of experiments be made, it will be proper, in all
cases, to let the gases remain together a definite time (say 10
minutes) before noting the diminution ; and it is needless to
SECT. II.
NITROUS GAS.
393
transfer them into another vessel. If the mixed gas, under
examination, contain much more oxygen than is present in
atmospherical air, then it is proper to dilute the nitrous gas
with an equal bulk of hydrogen gas ; and, in this case, the
narrower the tube in which the experiment is made, the more
accurate will be the result.
Subsequent experience has convinced me that the method,
proposed by Mr. Dalton, though sufficiently correct when
applied to a mixture of the same, or nearly the same, standard
as the atmosphere, cannot be relied on when the proportion
of oxygen is either considerably greater or less. In the former
case, the process gives too great a diminution, sometimes in¬
deed to such an extent as to indicate more oxygen gas than
the whole amount of what was submitted to experiment.
When the air, on which we are operating, is of an inferior
standard to the atmosphere, we do not learn its full propor¬
tion of oxygen. Notwithstanding these objections, however,
the method has considerable value, since it may be applied to
determine the proportion of oxygen in some mixed gases, to
which other eudiometrical tests are not applicable ; for exam¬
ple, to mixtures of hydro-carburet and oxygen gases.
The application of nitrous gas to eudiometrical purposes,
it has lately been contended by Gay Lussac, is susceptible of
perfect accuracy, provided certain precautions be observed
which he has pointed out, and which were suggested by his
theoretical views of the constitution of these gases. A narrow
tube he finds to be unfit for an eudiometer, his object being
to form nitrous acid gas, which is but slowly absorbed by
water. Instead therefore of a tube, we must take a wide ves^
sel, such as a small tumbler glass; and to 100 parts of atmo-
pheric air, previously measured, we must add at once 100
measures of nitrous gas. A red fume will appear, which will
soon be absorbed without agitation, and in half a minute, or a
minute at most, the absorption will be complete. Pass the
residuum into a graduated tube, and it will be found, almost
invariably, thut 84 measures have disappeared. Dividing this
number by 4, we have 21 for the quantity of oxygen con¬
densed.
By a series of experiments on mixtures of oxygen and ni-
2
394
NITROUS GAS*
CHAP. XIII.
trogen gases in various proportions, Gay Lussac found that
this eudiometricai process may be depended upon, whether
the oxygen exceed or fall short considerably of the proportion
contained in atmospheric air.
( g ) The generation of an acid, by the admixture of nitrous
gas with common air or oxygen gas, may be shown by the
following experiment. Paste a slip of litmus-paper within a
glass jar, near ihe bottom; and into the jar, filled with and
inverted in water, admit as much nitrous gas, previously well
washed, as will displace the water below the level of the
paper. The colour of the litmus will remain unchanged; but,
on adding atmospheric air or oxygen gas, it will be imme¬
diately reddened.
(h) The acid, thus produced, is either nitric or pernitrous,
according to the circumstances of the experiment, the pre¬
sence of water favouring the production of the latter, and its
absence promoting that of nitric acid #. The nature of the
product may be shown, in a general way, as follows : Into a
jar, filled with and inverted in mercury, pass a small quantity
of a solution of pure potash ; and, afterward, measures of oxy¬
gen and nitrous gases, separately, and in proper proportion.
On removing the solution from the jar, exposing it for some
time to the atmosphere, and afterward evaporating it, crystals
of nitrate of potash will be formed, a salt which is ascertained
to be formed of potash and nitric acid.
(i) Nitrous gas is absorbed by hydro-nitric acid, which, by
this absorption, is considerably changed in its properties.—
Transmit the gas, as it issues from the materials that afford it,
through colourless nitric acid. The acid will undergo suc¬
cessive changes of colour, till at last it will become orange-
coloured and fuming. In this state it is called nitrous acid,
because it contains a less proportion of oxygen than the colour¬
less nitric acid.
According to Dr. Priestley, 100 parts of nitric acid, of the
specific gravity of 14 to 10, absorb, in two days, 90 parts by
weight of nitrous gas f. When about seven parts of gas have
* Dalton, in Thomson's Annals, x. 39.
t Priestley on Air, 2d edition, i. 383. In the experiment alluded to.
SECT. ir.
NITROUS GAS.
395
been absorbed, the acid acquires an orange colour; when IS
have been absorbed, it becomes green ; and the whole quan¬
tity, which it is capable of condensing, changes it into a liquor,
which emits an immense quantity of red fumes. The gas, thus
absorbed, is mostly separated again on dilution with water.
(k) The nitrous gas, thus absorbed, is expelled again by a
gentle heat. This may be shown by gently heating the acid
coloured in Experiment i, till it again becomes limpid. In
this experiment light should be excluded.
(l) Nitrous gas is decomposed by exposure to bodies that
attract oxygen. Thus, iron filings decompose it, and become
oxydized, affording a proof of the presence of oxygen in this
gas. During this process, water, ammonia, and nitrous oxide,
in the proportion of one volume from two of nitrous gas, are
generated. Sulphuret of potash, &c., have a similar effect.
Sulphuret of barytes gives one half its volume of nitrogen.
Mixed with sulphurous acid, nitrous gas is decomposed, and
this acid is changed into the sulphuric, but not unless water is
present*. Nitrous gas does not with hydrogen gas afford
a mixture that can be exploded by the electric spark ; but
with ammoniacal gas it may be fired in a Volta’s eudiome¬
ter over mercury. The oxygen of the nitrous gas unites with
the hydrogen of the ammonia, and the nitrogen of both gases
is set at liberty.
Bodies that have a still more powerful affinity for oxygen
decompose nitrous gas into its ultimate elements. Charcoal
ignited in 100 measures, gives 50 measures of nitrogen gas,
and 50 of carbonic acid. Arsenic, zinc, or potassium, when
heated in it, evolve half its volume of nitrogen. Nitrous gas
should consist, therefore, of 1 volume of oxygen -f- 1 volume
one fifth of an ounce-measure of nitric acid absorbed 130 ounce-measures
of nitrous gas ; or more than 60 per cent, by weight. There is reason,
however, to suspect some inaccuracy in the experiment ; for according to
Sir H. Davy, 100 parts of nitric acid, after having absorbed all the nitrous
gas which it is capable of condensing, hold only nine or between nine and
ten parts in combination, and Mr. Dalton could not condense more than 20
times its bulk, or a little more than 2 per cent, by weight, of nitrous gas,
into acid of the specific gravity 1.3.
* Nicholson's Journal, xvii. 43.
396
NITROUS GAS.
CHAP. XIII.
of nitrogen, neither of which elements is in a state of condensa¬
tion. This, however, would lead to a determination of the
weight of the atom of nitrogen, very different from that already
deduced from the composition of ammonia and of nitric acid.
For if nitrous gas be constituted, as Mr. Dalton supposes, of
an atom of each of its elements, and if these exist in it in equal
volumes, the atom of oxygen will be to that of nitrogen as
33.8 to 29.5 (the proportions by weight in nitrous gas, accord¬
ing to this view of its composition) or as 7.5 to rather more
than 6.5, which last number would denote the weight of the
atom of nitrogen. I have, however, expressed my coincidence
in the opinion, that nitrous gas consists of one atom of nitro¬
gen and two of oxygen ; which would make the weight of the
atom of nitrogen 6.5 x 2 = 13.
(m) Nitrous gas and chlorine, when both perfectly dry,
have no action whatsoever on each other ; but, if water be pre¬
sent, there is an immediate decomposition, and nitrous and
muriatic acids are formed.
( n ) Nitrous gas is absorbed by the green sulphate and mu¬
riate of iron *, which do not absorb nitrogen gas. To ascer¬
tain, therefore, how much nitrogen gas a given quantity of
nitrous gas contains, let it be agitated in a graduated tube with
one of these solutions. This analysis is necessary, previously
to deducing, from its effects on atmospheric air, the proportion
of oxygen gas ; for we must subtract from the residuum the
quantity of nitrogen introduced by the nitrous gas.
From the important use which is now made in eudiometry
of this solution of nitrous gas in sulphate of iron, it may be
proper to describe the mode of its preparation.
Dissolve as much of the green sulphate of iron in water as
the water will take up, or dissolve iron filings in sulphuric
acid, diluted with five or six parts of wrater, leaving an excess
of the iron, in order to ensure the perfect saturation of the
acid. Fill a wide-mouthed bottle with this solution, invert it
in a cupful of the same, and into the inverted bottle receive
the nitrous gas, as it is generated by the proper materials,
shaking the inverted bottle frequently. The colour of this
# For an account of these salts, see chap, xviii. sect, 6.
SECT. II.
NITROUS GAS.
397
solution will change to black, and the production of gas and
the agitation are to be continued, till the absorption can be
carried no farther. The impregnated solution should be pre¬
served in a number of small bottles, not holding more than
an ounce or two each. The most commodious method of ap¬
plying this solution, is by means of Dr. Hope's eudiometer,
already described. (Chap. v. sect. 4.)
(o) A very interesting experiment, affording a synthetic
proof of the constitution of nitrous gas, was made by the Rev,
Dr. Milner, of Cambridge * *. Into an earthen tube, about 20
inches long and three fourths of an inch wide, open at both
ends, put as much coarsely powdered manganese as is suffi¬
cient nearly to fill it. Let this be placed, horizontally, in a
furnace, having two openings opposite to each other (fig. 40).
To one end of the earthen tube adapt a retort, containing a
strong solution in water of pure ammonia, and to the other a
bent glass tube, which may terminate in a two-necked empty
bottle. To the other neck of the bottle, lute a glass tube,
bent so as to convey any gas that may be produced, under the
shelf of the pneumatic trough. Let a fire be kindled in the
furnace ; and, when the manganese may be supposed to be
red-hot, drive over it the vapour of the ammonia. The alkali
will be decomposed ; its hydrogen, uniting with part of the
oxygen which is combined with the manganese, will form
water; while its nitrogen, uniting with another portion of the
oxygen, will constitute nitrous gas. The gas, thus generated,
may be collected by the usual apparatus.
(p) Another fact, showing the mutual relation of ammonia
and of the compounds of nitrogen, was discovered some years
ago by Mr. Wm. Higgins f. Moisten some powdered tin
(which is sold under this name by the druggists) with strong
nitric acid ; and, when the red fumes have ceased to arise, add
some quick-lime or solution of pure potash. A strong smell
of ammonia will be immediately produced.
In this experiment, the tin, at the same instant, attracts the
■OWipniy^m. - . ■ . . . . . ■ - . . . . . . w„.
* Phil. Trans. 1789.
f See his Comparative View of the Phlogistic and Antiphlogistic Theories,
3d edition, p, 300, note.
I
398 NITROUS OXIDE. CHAP. XIIJ.
oxygen both of the nitric acid and of the water. Hydrogen
and nitrogen are consequently set at liberty ; and, before they
have assumed the gaseous state, these two bases combine, and
constitute ammonia. The ammonia, thus generated, unites
with a portion of undecomposed nitric acid ; and is disengaged
from this combination by potash or lime, which render it evi¬
dent to the smell*
SECTION III.
Gaseous Oxide of Nitrogen . — Nitrous Oxide of Davy .
f. This compound, also consisting of oxygen and nitrogen,
but in different proportions from those of nitrous gas, may be
obtained by several processes.
(a) By exposing common nitrous gas for a few days to iron
filings, or to various other bodies strongly attracting oxygen,
this gas is changed into the nitrous oxide.
Some nicety and experience are required to suspend the de¬
composition before it has gone too far ; in which case nitrogen
gas is obtained. The sulphite of potash, being incapable of
decomposing nitrous oxide, is best adapted to the conversion
of nitrous gas into that elastic fluid. The process, in all cases,
may be suspended, when about two thirds the original bulk of
the gas are left.
(b) By dissolving zinc, or tin, in nitric acid, diluted with
five or six times its weight of water. Zinc, during this solu¬
tion, disengages nitrous oxide till the acid begins to exhibit a
brownish colour, when the process must be suspended, as ni¬
trous gas is then formed. But by neither of these processes
is the gas obtained sufficiently pure for exhibiting its qualities.
To procure it in a state of purity, the following process is the
best adapted.
(c) To nitric acid, diluted with five or six parts of water,
add carbonate of ammonia, till the acid is saturated. Then
evaporate the solution by a gentle heat ; and, to supply the
waste of alkali, add, occasionally, a little more of the carbo¬
nate. The salt obtained, after the solution has cooled, is next
to be put into a glass retort, and distilled with a sand-heat,
SECT. III.
NITROUS OXI»«a
S 99
not exceeding 440° Fahrenheit *. The heat of an Argand's
lamp is more than sufficient, and requires cautious regulation.
The salt will presently liquefy, and must be kept gently sim¬
mering, avoiding violent ebullition. The gas may be collected
over water, and allowed to stand a few hours before it is used,
during which time it will deposit a white substance, and will
become perfectly transparent,
A gazometer is best adapted for its reception ; because all
danger is then avoided of an absorption of the water of the
trough into the retort; and because the gas is brought into
contact with a much smaller surface of water, which has the
property of absording a considerable proportion of the gas.
On this account, water, which has been once used to confine
the gas, may be kept for the same purpose.
The changes that take place, during the conversion of ni¬
trate of ammonia into nitrous oxide, are the following : Nitric
acid is composed of oxygen and nitrous gas ; ammonia, of
hydrogen and nitrogen. In a high temperature, the nitrous
gas combines with an additional dose of nitrogen, and forms
nitrous oxide ; while the oxygen of the decomposed nitric
acid unites with the hydrogen of the ammonia, and forms
water. Water and nitrous oxide are, therefore, the only pos¬
sible results of the decomposition of nitrate of ammonia by heat.
The gas, thus obtained, was termed, by the Society of Dutch
Chemists, gaseous oxide of azote ; but, for the sake of brevity,
and as more conformable to the nomenclature of other com¬
pounds of nitrogen, I shall use, with Sir H. Davy, the name
of nitrous oxide f .
In order to ascertain whether nitrous oxide be adulterated
with either common air or oxygen gas, we may mix equal
measures of the gas under examination, and of nitrous gas.
If any diminution ensue, the presence of one of these may be
suspected ; and the amount will show which of them is eon™
* From the observations of Mr. Sadler (Nicholson’s Journal, xv. 286),
it appears that the purity of the nitrate of ammonia is of considerable im¬
portance ; and that its adulteration with muriate diminishes the quantity,
and impairs the quality of the gas.
f For a full account of this gas, consult Sir H, Davy’s Researches, Che¬
mical and Philosophical. London. Johnson, 1809.
400
NITROUS OXIDE.
CHAP. XIII.
tained in it. Nitrous gas, however, is a much more common
contamination ; for it is generated, along with nitrous oxide,
^whenever the temperature of the salt is raised too high. Its
presence may be detected, either by a diminution on the ad¬
mixture of oxygen gas ; or by an absorption being effected, on
agitating the gas with a solution of green sulphate of iron,
which has no action on pure nitrous oxide.
II. Nitrous oxide gas has the following properties :
(a) It is considerably heavier than common air. At about
55° Fahrenheit and 30 inches pressure, 100 cubic inches weigh
50.20 grains, or under the same pressure, and at 60° Fahren¬
heit 49.68. (Davy.) More recently Sir FI. Davy has stated
100 cubic inches to weigh between 48 and 49 grains, and
hence its specific gravity is very nearly 1.6. Colin makes it
only 1.5204, or, corrected by calculation, 1.5209. On the
theory that it is constituted of one volume of nitrogen, and
half a volume of oxygen, 100 cubic inches should weigh 46^
grains *.
( b ) A candle burns in it with a brilliant flame and crack¬
ling noise. Before its extinction, the white inner flame be¬
comes surrounded with an exterior blue one.
(c) Phosphorus, introduced into it in a state of inflamma¬
tion, burns with increased splendour.
Phosphorus, however, may be melted and sublimed in this
gas, without alteration. It may even be touched with red-hot
iron wire, without being inflamed; but when a wire intensely
heated, or made white-hot, is applied, the phosphorus burns,
or rather detonates, with prodigious violence.
(d) Sulphur, introduced into nitrous oxide when burning
with a feeble blue flame, is instantly extinguished; but when
in a state of an active inflammation, it burns with a vivid and
beautiful rose-coloured flame.
(c) Red-hot charcoal burns in it more brilliantly than in
the atmosphere. When the experiment is made in a proper
apparatus, the results of its combustion are found to be one
measure of nitrogen gas and half a measure of carbonic acid
(equivalent to half a measure of oxygen) from each measure
*
Dalton, Thomson’s Annals, ix. 190.
SECT. III.
NITROUS OXIDE.
401
of nitrous oxide. It must, therefore, consist of 59 parts by weight
of nitrogen and 33.8 oxygen *, or it must contain by weight
Oxygen ........ 36.43 .... 100 ... . 57.
Nitrogen . 63.57 . . . .174 . . . .100.
100. 274 157.
On the supposition that nitrous oxide is constituted of one
atom of nitrogen and one of oxygen, this would make the
weight of the atom of nitrogen = 13.4 ; for as 33.8 to 59, so
is 7.5 to 13.4.
(f) Iron wire burns in this gas with much the same appear¬
ance as in oxygen gas, but for a shorter period.
(g) Nitrous oxide is rapidly absorbed by water that has been
previously boiled, about one thirtieth the original bulk of the
gas remaining uncondensed. A quantity of gas, equal to
considerably more than nine-tenths the bulk of the water, may
be thus made to disappear. This property furnishes a good
test of the purity of nitrous oxide ; for the pure gas is almost
entirely absorbed by boiled water, which has cooled without
the access of air. The gas employed should exceed the wateT
three or four times in bulk, in order to obtain a saturated so¬
lution.
(h) Water, that has been saturated with this gas, gives it
out again, unchanged, when heated.
(£) The impregnated water does not change blue vegetable
colours.
( k ) It has a distinctly sweet taste, and a faint, but agreeable,
odour.
(/) Nitrous oxide is not diminished by admixture with
either oxygen or nitrous gas.
(m) A mixture of this gas with hydrogen gas detonates
loudly, on applying a lighted taper, or passing an electric
spark.
When the proportion of hydrogen is nearly equal to that
of nitrous oxide, or as 39 to 40, nitrogen gas only remains
after the explosion ; but when the proportion of hydrogen is
* Two hundred cubic inches of nitrogen gas weigh 59 grains, and 100 of
oxygen weigh 33.8.
VOL. I.
NITROUS OXIDE,
CHAP, XIII,
402
smaller, nitric acid is also generated. In general terms, it
may be stated that one measure requires one measure of hy¬
drogen gas, and leaves after combustion one measure of nitro¬
gen. Nitrous oxide forms, also (as I have shown, Philoso¬
phical Transactions, ] 809, page 444), a combustible mixture
with ammoniacal gas, 100 measures of the latter requiring for
saturation 1 30 measures of nitrous oxide.
(n) Nitrous oxide is not absorbed by alkalies ; but if it be
brought into contact with them, when in a nascent state, or
before it has assumed the form of a gas, it then enters into
combination with alkaline bases. Thus, when a mixture of
sulphite of potash and pure potash is exposed to nitrous gas,
the gas is disoxygenized by the sulphite, and changed into
nitrous oxide, which unites with the alkali. We obtain, there¬
fore, a mixture of sulphate of potash with a compound of
nitrous oxide and alkali, the former of which may be separated
by priority of crystallization. The latter is composed of about
three parts of alkali, and one of nitrous oxide. It is soluble
in water ; has a caustic taste, of peculiar pungency ; and con¬
verts vegetable blues to green. Powdered charcoal, mingled
with it, and inflamed, burns with bright scintillations. The
nitrous oxide is expelled from fixed alkalies by all acids, even
by the carbonic.
(o) Animals, when wholly confined in this gas, die speedily.
(p) One of the most extraordinary properties of this gas is
exhibited by its action on the human body, when received into
the lungs. When thus employed, it does not prove fatal, be¬
cause, when received into the lungs, it is mixed and diluted
with the atmospherical air present in that organ. To admi¬
nister the gas, it may be introduced into an oiled silk bag or
clean bladder, furnished with a stop-cock, and may be
breathed repeatedly from the bag and back again, as long as
it will last. The sensations that are produced vary greatly
in persons of different constitutions; but, in general, they are
highly pleasureable, and resemble those attendant on the plea¬
sant period of intoxication. Great exhilaration, an irresistible
propensity to laughter, a rapid flow of vivid ideas, and an
unusual fitness for muscular exertion, are the ordinary feel¬
ings it produces. These pleasant sensations, it must be added,
SECT. IV.
NITROUS ACID.
403
are not succeeded, like those accompanying the grosser eleva¬
tion from fermented liquors, by any subsequent depression of
nervous energy*
SECTION IV.
Nitrous Acid .
It has been a subject of controversy whether an acid, en¬
titled to this denomination, and holding the same relation to
the nitric, which the sulphurous bears to the sulphuric, has
really existence. That the acid, obtained from nitre, has dif¬
ferent states of oxygenation, and contains a less quantity of
oxygen in proportion to the depth of its colour, is generally
admitted. But it has been contended that we are to consider
all these varieties as nitric acid, holding in combination va¬
riable proportions of nitrous gas ; and the principal argument
in favour of this theory is that the substance, occasioning the
colour, may be separated by the mere application of heat.
Sir H. Davy, in the year 1800, gave the following table, show¬
ing the proportion of nitrous gas in nitrous acid of different
colours.
100 parts by weight contain
Sp. Gr. Real Acid. Nit. Gas. Water.
Pale yellow ....... .1.502 . . . .90.5 ... .1-2 ... .8.3
Bright ditto . ...... 1 .50 • 0 . .88.94 . . , .2.96 ... .8.1
Dark orange . 1.480 . . . .86.84 . . . .5.56 . . . .7.6
Light olive ....... .1.479 . . . .86. . . . .6.45 . . . .7.55
Dark olive . 1.478 _ 85.4 ....7.1 ....7.50
Bright green . . 1.476 ... .84.8 ... .7.76 ... .7.44?
Blue green . . . .1.475 . . . .84.6 ... .8. ... .7.40
Mere dilution with water is sufficient to vary these colours.
Thus the dark orange-coloured acid, by dilution, passes
through the shades of blue, olive, and bright green. Nitric
acid, also, by absorbing nitrous gas, has its specific gravity
diminished. Colourless acid, for example, when rendered of
pale yellow, becomes lighter in the proportion of 1.51 to 1.502.
It is now, however, generally admitted that the nitrous acid
2 D 2
NITROUS ACID.
CHAP. XIII.
404
is as much a distinct and peculiar compound as any other of
the compounds of nitrogen.
The proportions of its elements have been investigated by
Sir H. Davy *, who finds that two measures of nitrous gas
and one of oxygen, ( = 1 volume of nitrogen and 2 of oxygen),
both freed from moisture, and mixed together in a vessel pre¬
viously exhausted of air, are condensed into half their
volume +, and form a deep orange-coloured elastic fluid, which
may be called nitrous acid gas . It has the following proper¬
ties t
A taper burns in it with considerable brilliancy. Sulphur
inflamed does not burn in it ; but phosphorus burns vividly.
Charcoal continues to burn in it with a dull red light. Water
absorbs it, and gains a tint of green. It reddens litmus paper,
has a sour taste, a strong smell, and turns animal substances
yellow. One hundred cubic inches, calculating from the con¬
densation of its elements assumed by Davy, must weigh 65.3
grains, at mean temperature and pressure, and it must contain
in 100 grains,
Nitrogen ..... .30.32 . . , .100
Oxygen . ..... .69.68 . . . .230
100.
To form liquid nitrous acid, nothing more is necessary
than to saturate water with this vapour. The water becomes
first green, then blue, and finally an orange colour more or
less deep. The latter may be brought to the state of green or
blue by adding more or less water. Hence the colour depends
merely on the circumstance of density.
The properties of liquid nitrous acid, Berzelius remarks J,
differ from those of nitric acid; for while the latter boils at
236°, nitrous acid of the same density boils at 160°. The
purely acid part he considers to be composed of 36.9 nitrogen
-f 63.1 oxygen. With bases, it forms a class of salts, which,
he asserts, differ entirely from those containing nitric acid.
* Elements of Chem. Philosophy.
f Gay Lussac states the condensation at two thirds of the volume of the
mixture. Ann. de China, et Phys. i. 403.
f 13 Ann. de China, 10.
SECT. V.
PER-NITROUS ACID®
405
On the other hand, we have the testimony of Gay Lussac that
the nitrous acid is decomposed with so much facility by con¬
tact with alkaline solutions, as to be incapable of forming a
distinct class of salts. With solution of potash, for example,
he found that it affords pernitrate and nitrate, but nothing
that can properly be called a nitrite of potash *,
SECTION V.
Of Per-nitrous Acid .
When 400 measures of nitrous gas and 100 measures of
oxygen (in which the nitrogen and oxygen are to each other
by measure as 100 to 150) are mixed together over a solution
of potash confined by mercury, we obtain 100 measures of a
compound, called by Gay Lussac per-nitrous acid f . Mr.
Dalton, who obtained it several years ago, and then consi¬
dered it as nitrous acid, has lately proposed to call it sub-nitrous
acid J ; but the name suggested by Gay Lussac seems to me
more conformable to analogy, since the new acid differs from
nitrous acid in containing an additional proportion of nitro¬
gen, This new compound is so far hypothetical, that it has
never yet been exhibited in a separate form ; for when a
stronger acid is added, to expel it from the potash, it is re¬
solved into nitrous gas and nitrous acid.
Per-nitrous acid is, also, frequently generated, when nitrous
and oxygen gases, or nitrous gas and common air, are min¬
gled together in eudiometrical processes. At the same time
nitrous and nitric acids are produced in proportions to the
per-nitrous and to each other, which are modified by the
circumstances of the experiment §.
Calculating from the proportions of its elements and their
state of condensation, 100 cubic inches of per-nitrous acid
gas must weigh 80.2 grains ; and it must consist in 100 grains
of
* Ann. de Chim. et Phys. i. 409. f Ibid. i. 400.
I Thomson’s Annals, vol. ix. § Dalton, Thomson’s Annals, x. 63.
406
NITRATES.
CHAP. XIII.
Nitrogen . . 42.02 .... 100 ... . 72.5
Oxygen ........ 57.98 . . . . J 37 . . . .100.
100.
Per-nitrous acid unites with sulphuric acid, either concen¬
trated or a little diluted, and, at a moderate temperature, the
compound forms elongated four-sided prisms. These crystals,
and even the liquid in which they are formed, give nitrous
gas when brought into contact with water. A similar solid is
obtained by passing nitrous acid vapour into sulphuric acid;
and it appears, also, to be identical with the crystalline solid
formed by Clement and Desormes by the mixture of oxygen
gas, sulphurous acid, nitrous gas, and the vapour of water.
The last-mentioned compound had been supposed to consist of
nitrous gas and sulphuric acid ; but sufficient reasons have
been given by Gay Lussac for the new view of it, which has
just been stated.
SECTION VI.
Nitrates .
Art. 1 . — Nitrate of Potash ,
I. A direct synthetic proof of the composition of this salt
may be obtained by saturating nitric acid with potash, either
pure or in a carbonated state. The solution, on evaporation,
yields crystals of nitrate of potash, or nitre.
For the purposes of experiment, however, the nitrate of
potash, which may be met with in the shops, and which is an
abundant product of nature, may be employed on account of
its greater cheapness. The nitre, which is met with as an
article of commerce, is brought to this country, chiefly from
the East Indies. When it arrives it is a very impure salt,
containing, besides other substances, a considerable propor¬
tion of muriate of soda. In this state it is called rough nitre.
For the purposes of chemistry, it requires to be purified by
solution in water and re-crystallization ; and it then obtains
the name of refined nitre, or refined saltpetres
1
SECT. VI.
NITRATE OF POTASH.
40?
II. This salt has the following properties :
(a) It crystallizes in prismatic octahedrons, generally con¬
stituting six-sided prisms, terminated by two-sided summits.
It contains, according to Berzelius, no water of crystallization.
Thenard has determined that it consists of
49.5 potash
50.5 nitric acid.
But as potash itself, in the driest form under which we can
procure it, still contains water, Berthollet has given the fol¬
lowing proportions as those of nitrate of potash :
50.1 potash
49.9 acid
100.*
These proportions are nearly reversed by Berard, who
makes it consist of 48.64 base and 51.36 acid f . The pro¬
portions, deduced by Dr. Wollaston, are 46.67 base to 53.33
acid: and those by Dr. Ure 4? base and 53 acid.
( b ) For solution, it requires seven times its weight of
water at 60° of Fahrenheit; and boiling water takes up its
own weight. This is the degree of solubility assigned by
Bergman ; but La Grange asserts, that, at the ordinary tem¬
perature, nitrate of potash requires only three or four times
its weight of water for solution ; and half its weight of boiling
water
( c ) By the application of a moderate heat it fuses, and
being cast in moulds, forms what is called Sal Prunelle*,
After fusion, Sir FI. Davy found that it still yielded water,
when distilled with boracic acid.
(d) If a red-heat be applied, nitrate of potash is decom¬
posed in consequence of the destruction of its acid. By dis¬
tilling it in an earthen retort, or in a gun-barrel, oxygen gas
may be obtained in great abundance, one pound of nitre
yielding about 12,000 cubic inches, of sufficient purity tor
common experiments, but not for purposes of accuracy.
* Mem. d’Arcueil, iii. 170.
X Manuel, 1st edition, i. 243.
f 71 Ann, de China. 69,
NITRATES#
CIIAP. XII f.
408
(e) Nitrate of potash, that has been- made red-hot, seems
to contain an acid less oxygenated than the common nitric
acid, and having a weaker affinity for alkalies. For if acetic
acid be poured on nitre that has been thus treated, the nitrous
acid is expelled in red fumes, whereas common nitre is not at
all affected by acetic acid.
(/) Nitrate of potash is rapidly decomposed by charcoal
in a high temperature. This may be shown, by mixing two
parts of powdered nitre with one of powdered charcoal, and
setting fire to the mixture in an iron vessel under a chimney.—
The products of this combustion, which may be collected by
a proper apparatus, are carbonic acid and nitrogen gases.
Part of the carbonic acid also remains attached to the resi¬
duary alkali, and may be obtained from it on adding a stronger
acid.
This residue was termed, by the old chemists, clyssus of
nitre.
(g) Nitrate of potash is also decomposed by sulphur, and
with different results according to the temperature and pro¬
portions employed.
1. Mix powdered nitre and sulphur, and throw the mix¬
ture, by a little at a time, into a red-hot crucible. The sul¬
phur will unite with the oxygen of the nitric acid, and form
sulphuric acid ; which, combining with the potash, will afford
sulphate of potash. The production of the latter salt will be
proved by dissolving the mass remaining in the crucible and
crystallizing it, when a salt will be obtained exhibiting the
characters described, chap. xii. sect. 4.
2. Mix a portion of sulphur with one sixth or one eighth
its weight of nitrate of potash ; put the mixture into a tin
cup, and raise it, by a proper stand (fig. 25), a few inches
above the surface of water, contained in a flat shallow dish.
Set fire to the mixture, and cover it with a bell-shaped re¬
ceiver. In this case, also, sulphuric acid will be formed ; but
it will not combine, as before, with the alkali of the nitre,
which alkali is present in sufficient quantity to absorb only a
part of the acid produced. The greater part of the acid will
be condensed on the inner surface of the glass bell, and by
the water, which will thus become intensely acid. The ope-?
SECT. VI.
NITRATE OF POTASH.
409
ration may be repeated three or four times, using the same
portion of water. When the water is partly expelled, by eva¬
poration in a glass dish, concentrated sulphuric acid remains,
which has been formed by the union of the oxygen of the
nitre, and that of the atmospherical air, with the sulphur
submitted to experiment. By a process of this kind, con¬
ducted on a large scale, and in extensive leaden chambers, the
sulphuric acid of commerce is prepared. The dilute acid,
resulting from the union of the condensed vapour of the
burning materials, with the stratum of water at the bottom of
the chamber, is first boiled down in part in shallow leaden
vessels, and is then transferred into glass retorts, where it is
farther concentrated by the continued application of heat.
In a memoir of Clement and Desormes, published in
Nicholson’s Journal, xvii. 41, it is proved, that the nitre does
not furnish above one tenth part of the oxygen, required for
the conversion of sulphur into sulphuric acid, and that the
rest of the oxygen is derived from the atmospherical air of the
chamber. Sulphurous acid, they suppose, is in the first in¬
stance formed by the combustion of tire sulphur ; and, at the
same moment, nitrous gas is evolved from the de-oxygenation
of the nitric acid contained in the saltpetre. This nitrous
gas, uniting with the atmospheric oxygen, composes nitrous
acid gas , which, when water is present, has the property of
converting sulphurous into sulphuric acid, and of returning,
at the same time, to the state of nitrous gas. The same
process is repeated, and thus the same portion of nitrous gas
acts repeatedly as an intermedium between the sulphur, pre¬
viously changed into sulphurous acid, and the atmospheric
ox}Tgen.
( h ) A mixture of three parts of powdered nitre, two of
carbonate of potash, or common salt of tartar, and one part
of sulphur, all accurately mixed together, forms the fulmi¬
nating powder , which explodes with a loud noise, when laid
on an iron heated below redness.
(i) A mixture of five parts of powdered nitre, one part of
sulphur, and one of powdered charcoal, composes gunpowder .
The materials are first very finely powdered separately, then
mixed up together, and beaten with a wooden pestle, a siiffi-
2
410
NITRATES.
CHAP. XIII,
cient quantity of water being added to prevent an explosion.
The mixture is afterward granulated, by passing through
sieves, and dried very cautiously *.
Process for preparing Nitric Acid .
Nitrate of potash is decomposed by sulphuric acid, which
combines with the potash, and expels the nitric acid. Put
into a glass retort, which may be either tubulated or not, four
parts of nitrate of potash, reduced to a coarse powder, and
pour upon it three parts of concentrated sulphuric acid.
Apply a tubulated receiver, of large capacity, between which,
and the retort, an adopter may be interposed ; these junctures
being luted with a mixture of pipe-clay, sifted sand, and cut
tow or flax. — To the tubulure of the receiver, a glass tube
may be fixed by means of the fat lute, and may terminate in
another large receiver, containing a small quantity of water.
If the operator wishes to collect the gaseous products also,
this second receiver should be provided with a tubulure, to
which a bent pipe may be luted, terminating under one of the
inverted funnels in the shelf of the pneumatic trough. Apply
heat to the retort, through the intervention of a sand-bath.
The first product that passes into the receiver, is generally of
a red colour, and of a smoking quality. These appearances
gradually diminish; and if the materials used were clean, the
acid will come over pale, and even colourless. Afterwards
it gradually re-assumes a red colour, and smoking property ;
which appearances go on increasing till the end of the opera¬
tion; and the whole product, mingled together, has either a
yellow or an orange colour, according to the temperature
employed.
The proportions recommended in the new London Phar¬
macopoeia for the preparation of nitric acid are two pounds
of nitrate of potash, deprived by heat of its water of crystal¬
lization, and two pounds of sulphuric acid. These are directed
to be mixed in a glass retort, and distilled in a sand-bath,
until a red vapour arises. The acid in the receiver is to be
* On the preparation of gunpowder, and the theory of its detonation,
consult Nicholson’s Journal, xxiii. 27?.
SECT. VI.
NITRATE OF POTASH.
411
mixed with an ounce of nitrate of potash, and again distilled
in a similar manner. After the second distillation its specific
gravity is 1.500; and one fluid-ounce, Mr. Phillips finds, de¬
composes 476 grains of marble. But he objects to the propor¬
tion of sulphuric acid, in the process of the College, as un¬
necessarily large. If, however, it be required to decompose
the whole of any portion of nitre, it is necessary to use as
much sulphuric acid, as will form, with the alkali of the
nitre, super sulphate of potash, viz. 97 parts of acid, of den¬
sity 1.85, to 100 parts of nitre.
The nitric acid, which first passes over, has the greatest
specific gravity. In an experiment of Dr. Perceval of Dublin,
the product wais taken in three portions; the first of which
had the specific gravity of 1.494, the second of 1.485, and
the third of 1.442*. Gay Lussac, by two successive distilla¬
tions of nitric acid of specific gravity 1.8 from four times its
weight of sulphuric acid, brought it to the density of 1.510.
In this state, he found it to be decomposed by heat or light
with extraordinary facility f.
In the large way, and for purposes of the arts, it is usual
to substitute earthen or cast-iron retorts, made extremely thick,
for those of glass. An earthen head is adapted, and this is
connected with a range of proper condensers. The strength
of the acid is varied also, by putting more or less water into
the receiver. What is called double aqua fortis varies in its
specific gravity from 1.3 to 1.4.
Nitric acic, obtained by this process, is never perfectly pure.
It contains, generally, both sulphuric and muriatic acids ; the
former of which is indicated by a white precipitate, on adding
a solution of nitrate of barytes to a little of the acid, diluted
with 8 or 10 parts of water; and the latter, by a milkiness
produced by nitrate of silver. The sulphuric acid may be
separated, either by a second distillation from a portion of
very pure nitre, equal in weight to one eighth of that ori¬
ginally employed, or by adding nitrate of barytes ; allowing
the precipitate to settle ; decanting the clear liquid, and dis^.
* Transactions of the Irish Academy, iv, 37.
f Ann. de Chim, et Phys. vol, i.
NITRATES.
CHAP. XIII.
4 1 2
tilling it. Muriatic acid is separated by the addition of nitrate
of silver. An immediate milkiness ensues, and fresh addi¬
tions must be made of nitrate of silver, as long as it occasions
this appearance. Then allow the precipitate to subside ; de¬
cant the clear liquid, and re-distil it ; leaving one eighth or
one tenth in the retort. The product will be pure nitric acid.
Nitrate of lead may be substituted for nitrate of silver The
nitric acid may also be obtained free from muriatic acid, if a
perfectly pure nitrate of potash be employed for distillation.
This purification is effected by repeated solutions of the nitre,
in boiling distilled water, and re-crystallizations.
Nitric acid obtained in this manner is deficient also in
another respect ; for it is not perfectly oxygenated, but holds
in solution a considerable quantity of nitrous acid. To expel
the latter, put the acid into a retort, to which a receiver is
applied, the two vessels not being luted, but joined merely by
paper. Apply a very gentle heat for several hours to the re¬
tort, changing the receiver as soon as it becomes filled with
red vapours. The nitrous gas will thus be expelled, and the
acid will remain in the retort in a state of purity, and as
limpid and colourless as water. It must be kept in a bottle
secluded from the liffht.
o
One hundred parts of nitrate of potash, according to La
Grange, yield by this process 43 of acid, or, according to my
experience, above 50 ; but, if the process of the College be
followed, 100 of fused nitre afford about 66-4 of acid. Even
this, however, is not the whole of what was contained in the
salt ; for a part is decomposed by the temperature necessary to
the operation. Accordingly, a large quantity of oxygen gas
is disengaged during the distillation, and may be collected by
an obvious addition to the apparatus.
In the retort, there remains a compound of potash with
more sulphuric acid than is essential to its saturation, or a
super-sulphate of potash. On submitting this to a pretty
strong heat, the excess of sulphuric acid is expelled ; and the
residue, dissolved and evaporated, affords crystallized sul¬
phate of potash.
* See Nicholson's Journal, xi. 134.
SECT. VI. NITRATES OF SODA AND AMMONIA. 41 3
Art. 2 . — Nitrate of Soda .
I. This salt may be formed, by saturating carbonate of
soda with nitric acid ; or by distilling common salt with three
fourths its weight of nitric acid. When the former process
is adopted, the solution must be evaporated, till a pellicle
appears on its surface, and then allowed to cool. Crystals
will be produced, having the shape of rhomboids, or rhom-
boidal prisms.
II. These crystals have a taste like that of saltpetre, but
more intense. They are soluble in three parts of water at
60°, and in less than an equal weight of boiling water*
They attract moisture from the atmosphere. In other re¬
spects, in the means by which their decomposition is effected
and its results, they agree with the nitrate of potash. The
only use of nitrate of soda is, perhaps, that which has been
suggested by Proust, who has found it to be more economical
in the making of fire-works than nitrate of potash It
consists, according to Dalton, of
57.6 acid
42.4 base
100.
Art. 3.-— Nitrate of Ammonia.
I. The most simple mode of preparing this salt is by adding
carbonate of ammonia to dilute nitric acid, till saturation has
taken place. If the liquor be evaporated, by a heat between
70° and 100°, to a certain extent, it shoots, on cooling, into
crystals, having the shape of six-sided prisms, terminated by
long six-sided pyramids. Evaporated at the temperature of
212°, it yields, on cooling, thin fibrous crystals; and when the
evaporation is carried so far, that the salt immediately concretes
on a glass rod by cooling, it then forms a compact and shapeless
mass.
II. The solubility of this salt varies, according to the tem¬
perature in which it has been formed. When in crystals, it
* Nicholson’s Journal, xv. 252. See also 6 Ann. de Chim. et Phys. 205.
414
NITRATES.
CHAP. XIII.
requires twice its weight of water, for solution, or half its
weight of boiling water. It deliquiates, in all its forms, when
exposed to the atmosphere.
III. The most important propert}7 of this salt is the one
which has been already described, viz. of yielding, when de¬
composed by heat, the nitrous oxide. One pound of the
compact kind gives, by careful decomposition, nearly five
cubic feet of gas, or rather more than 34 doses; so that the
expense, estimating the salt at 5s. 10 d. the pound, is about
2d. for each dose.
IV. In a temperature of 600° this salt explodes, and is
entirely decomposed. Hence it was formerly called nitrum
jiammans.
V. Its composition varies according to the mode of its pre¬
paration, and is stated by Sir H. Davy as follows:
Prismatic. Fibrous. Compact.
69.5 _ .... 72.5 . . . 74.5 acid
18.4........ 19.3 . 19.8 ammonia
12.1 . 8.2 . 5.7 water
100. 100. 100.
The prismatic variety is stated by Berzelius who inves¬
tigated very carefully the results of its decomposition, to con¬
sist of
67.625 acid
21.143 base
11.232 water
e ‘ " 1 ""1 i
100.
Art. 4. — Nitrate of Barytes.
Nitrate of barytes may be prepared, by dissolving either
the artificial or native carbonate in nitric acid, diluted with
eight or ten parts of water. If the artificial carbonate be
employed, it should be previously well washed with distilled
water, till the washings cease to precipitate nitrate of silver, ,
A solution of nitrate of barytes, mixed with one of silver,
* 80 Ann, de Chim. 182.
SECT. VI.
415
NITRATES OF STRONTJTES AND LIME.
should continue perfectly transparent. On evaporation, it
yields regular octahedrons, often adhering to each other in
the form of stars ; and sometimes it is obtained in small bril¬
liant plates. It requires for solution 12 times its weight of
water at 60°, and three or four parts of boiling water. It is
not altered by exposure to the air. In a red-heat, its acid is
decomposed, and the earth remains pure. This furnishes
another method of procuring pure barytes; but the heat must
not be carried too far, otherwise the barytes is apt to vitrify
with the crucible. The residue, on the addition of water,
dissolves with great heat and noise, and the solution, on cool-
ing, yields crystals of pure barytes.
Nitrate of barytes is composed, in 100 parts, according to
Clement and Desormes, of 60 base, and 40 acid and water.
Mr. James Thomson states its composition to be
59.3 barytes
40.7 acid and water.
This scarcely differs from the determination of Berzelius,
viz. 58.46 base -f- 41.54 acid, and no water.
Art. 5. — Nitrate of Sirontites .
This salt may be obtained' in the same manner as the nitrate
of barytes, with which it agrees in most properties. The
solubility of its crystals, however, differs considerably; for
they are dissolved by their own weight of water at 60°, or by
little more than half their weight of boiling water. When
applied to the wick of a candle, or added to boiling alcohol,
they communicate to the flame a deep blood-red colour*
They are decomposed by a high temperature, and afford pure
strontitic earth. Exclusive of water, the salt consists, ac¬
cording to Richter, of 51.4 acid + 48.6 base; or, according
to Stromever, of 50,62 acid + 49.38 base.
Art. 6. — Nitrate of Lime ,
This salt is found abundantly in the cement of old build-
ings, which have been long inhabited. To prepare it arti-
416
NITRATES,
CHAP. X1M
ficially, nitric acid, diluted with five or six parts of water,
may be saturated with carbonate of lime, 63 parts of which
are decomposed by 90.23 of nitric acid of density 1.5, and
give 103.05 of dry nitrate of lime*. When this solution is
boiled down to the consistence of syrup, and exposed in a
cool place, long prismatic crystals are formed, resembling, in
their disposition, bundles of needles diverging from a com¬
mon centre. These crystals are readily soluble in water, of
which, at 60°, they require two parts, and boiling water dis¬
solves an equal weight. They deliquiate speedily, when ex¬
posed to the air ; and are decomposed at the temperature of
ignition. Exclusive of water, it contains,
Acid. Base.
According to Dalton . . . . . 61.3 38.7
- — — — =» Phillips . 65.6 34.4
When a solution of nitrate of lime is evaporated to dryness
in an earthen vessel, then fused for five or ten minutes in a
crucible, and poured, while in fusion, into an iron pot pre¬
viously heated, the congealed mass forms Baldwin's phosphorus .
It must be broken into pieces, and preserved in a well-stopped
phial. These pieces, after having been exposed to the sun for
a few hours, emit in the dark a beautiful white light, affording
one variety of solar phosphorus.
Art. 7. — Nitrate of Magnesia.
This compound may be prepared, by dissolving carbonate
of magnesia in diluted nitric acid. The solution, when eva¬
porated, yields crystals in the shape of prisms, with four
oblique faces truncated at their summits. Most commonly,
however, it forms a shapeless mass, consisting of an immense
number of small needle-shaped crystals, crossing each other
irregularly. These crystals deliquiate in the air, and are
soluble in half their weight of water. When exposed to the
heat of ignition, they fuse ; a few bubbles of oxygen gas first
escape; and the nitric acid then passes undecomposed. The
salt contains, exclusive of water, according to Dalton, 69 acid
-f 31 base.
* Phillips, Journal of Science, v, 167.
SECT. VI.
NITRATES.
Art. 8.- — Nitrate of Alumine*
This salt is but little known. It may be formed by the
solution of fresh precipitated alumine, which has been w li
washed with distilled water, but not dried, in diluted nitric
acid, with the assistance of heat. The solution, which has
always an excess of acid, after evaporation, crystallizes in thin
ductile plates. The crystals are extremely soluble; and, on
the application of a high temperature, abandon their acid.
They are decomposed by most alkalies and earths. Pure pot¬
ash, added in excess, re-dissolves the precipitate.
Art. 9. — Nitrate of Glucine .
The nitrate of glucine is a sweet tasted salt, which cannot
be brought to crystallize. When evaporated to dryness, it
rapidly absorbs moisture from the atmosphere. It is soluble
in alcohol. A high temperature decomposes it, without
effecting its previous fusion.
Art. 10.— Nitrate of Zircon*
The nitric acid dissolves, but cannot be saturated with, fresh
precipitated zircon. The solution has always an excess of
acid. When evaporated, it forms a yellowish transparent
mass, extremely tenacious and viscid, and difficultly dried.
It has a styptic astringent taste, and leaves on the tongue a
thick substance, in consequence of its partial decomposition
by the saliva. This dry nitrate is extremely soluble. The
solution is decomposed by sulphuric acid, and by carbonate
of ammonia, which throw down a precipitate soluble in an
excess of the acid, or of the carbonate. Tincture of galls
forms a white precipitate, which is soluble in an excess of the
tincture.
Art. 11. — Nitrate of Ytlria
May be prepared by dissolving yttria in nitric acid. The
solution has a sweetish astringent taste ; and, in most proper¬
ties, resembles nitrate of glucine. It can scarcely be ob»
VOL, I, 2 E
41 8
NITRITES
CHAfc XIII.
fcained in crystals ; and if too great a beat be applied during
evaporation, the salt becomes soft, assumes the appearance of
honey, and concretes, on cooling, into a hard stony mass.
Exposed to the air, it attracts moisture, and is resolved into
& liquid*
SECTION VII.
Nitrites .
The easiest mode of obtaining the salts, which by some
have been considered as nitrites, is to deprive the acid, con¬
tained in the nitrates, of part of its oxygen, by exposure for
a short time to the temperature of ignition. This method, it
must be obvious, cannot be used with those nitrates that
abandon their acid on the application of heat, or which, like
nitrate of ammonia, are completely decomposed.
Nitrate of potash, after ignition in a crucible, emits, when
powdered, a smell of nitrous gas. When diluted nitric acid,
or even acetic acid, is poured upon it, vapours of nitrous acid
are disengaged ; and hence it appears, that the affinity of this
acid for its base is weakened by partial dis-oxygenation ; for
no such effect arises on adding these acids to the nitrate.
The solution of the salt in water changes the syrup of violets
to green. Its other properties are little known.
It has, however, been already stated in the section on ni¬
trous acid, that the existence of such a class of salts as the
nitrites is extremely questionable.
CHAPTER XIV.
MURIATIC ACID— -OXYMURIATIC ACID OR CHLORINE — AND
THEIR COMPOUNDS.
There are few subjects) respecting wliich the opinions of
chemists have undergone such frequent changes, as concerning
the nature of chlorine. The view originally taken by Scheele,
the illustrious discoverer of this substance, was, that the mu¬
riatic acid is a compound of a certain base and an imaginary
principle called phlogiston ; and that by the action of certain
bodies, it becomes dephlogisticated , or deprived of that sup™
posed principle of inflammability *. It was afterwards found,
however, that all bodies, which are capable of producing this
change in muriatic acid, contain oxygen, and that their pro¬
portion of oxygen is diminished by the process. It appeared,
therefore, to be an obvious conclusion, that what takes place
in the action of metallic oxides on muriatic acid is simply the
transference of oxygen from the oxide to the muriatic acid ;
and conformably with this theory, the resulting gas received the
name of oxy -muriatic acid . Sir H. Davy was led, by his ear¬
lier experiments, to modify, in some degree, this view of the
theory of the operation ; and to consider the muriatic acid as a
compound of a certain basis with water, and the oxy-muriatic
as a compound of the same basis with oxygen. This modifi¬
cation was rendered necessary by the fact, that when a me¬
tallic oxide is heated in muriatic acid gas, oxymuriatic acid is
obtained, and water appears in a separate state ; it was evi¬
dent, therefore, that muriatic acid gas must either contain
water ready formed ; or the elements of water ; or hydrogen,
capable of composing water with the oxygen of the oxide.
But, at a subsequent period, that distinguished philosopher
was induced, by the experiments of Gay Lussac and Thenard,
as well as by his own, to form a different theory on the sub¬
ject. Oxymuriatic acid, he now considers as a simple or un-
* On Manganese, § xxiih xxiv.
2 E 2
420
MURIATIC ACID*
CIIAF. XIV
decompounded substance ; and muriatic acid, as a compound
of that simple substance with hydrogen. To convert the mu¬
riatic acid into chlorine, we have only, according to this view,
to abstract hydrogen from the muriatic acid ; and this, it is
supposed, is all that is .effected by the action of those oxides,
which are adapted to the purpose. Again, to convert chlorine
Into muriatic acid, we have only to supply it with hydrogen ;
and accordingly the simple mixture of one measure of each
of those gases, when exposed for a short time* to the sun’s
rays, or exploded by an electric spark, affords two measures
of muriatic acid gas.
The oxymuriatic acid or chlorine (as Sir H. Davy proposes
to call it, in order to avoid all connection of its name with
hypothetical views) is supposed, also, to unite at once with the
metals, without requiring, like the sulphuric or nitric acid*
that the metals should first be in the state of oxides. In proof
of this theory, it appears to be sufficiently established, that
no oxygen can be obtained either alone, or in combination
with combustible bodies added for the purpose, from the com¬
pounds of chlorine and metals. The analyses, however, of
the metallic muriates, as they were formerly considered, re¬
main unimpeached by this change of theory. All that is ne¬
cessary, to transmute in idea a muriate into a compound of
chlorine, is to deduct the oxygen from the metallic oxide,*
and, adding it to the muriatic acid, to consider the sum as
chlorine. For example, muriate of soda, deprived of all
water, consists
On the oid theory, of muriatic acid ..... . 46
Soda composed of . . . . { j } 54
100.
\ “ *
On the new theory it consists of
Sodium . . . . . . . -40.5
Chlorine, 46 + 13.5= . . 59.5
100.
It Is remarkable that there is hardly any fact, connected
SECT. I.
CHLORINE WITH HYDROGEN.
421
with the chemical history of chlorine and muriatic acid, that
does not admit of being equally well explained upon the hy-
pothesis that chlorine is a compound., as upon that of its being
a simple substance. On the whole, however, the probabilities
certainly appear to me very much in favour of the new, or
rather the revived opinion of its elementary nature; especially
since the discovery of iodine. But there are still objections t©
its implicit adoption, which this is not the proper occasion to
state. I shall only observe, that not the least important of these
objections is, the instantaneous conversion, which the theory of
Bhlorine supposes, of the metallic combinations of that body
into muriates, when they are dissolved in water, the oxygen of
which is imagined to pass, in a moment, to the metal, while
the hydrogen is attracted by the chlorine. In the present
state of the inquiry, indeed, we stand in need of some fact,
which will admit of explanation only on one of the opposed
theories ; and shall serve the purpose of an experimentum
crucise
SECTION I.
Compound of Chlorine with Hydrogen .
Chlorine unites with hydrogen either silently or with deto¬
nation, accordingly as the experiment is conducted,
1. Let a phial, provided with a well-ground stopper, ,be
completely filled with a mixture of hydrogen and chlorine
gases in exactly equal bulks. Put the stopper into its place,
and keep the bottle, 24 hours, inverted with its mouth under
water. On withdrawing the stopper under water, nearly the
whole of the gas will have disappeared : and the remainder
will be absorbed by the contact of the water.
2. Mingle, in the detonating tube (fig. 28 or 29), equal
volumes of hydrogen and chlorine gases. When an electric
spark is passed through the mixture, a detonation will ensue,
and nearly the whole will be absorbed. But if the gases have
been carefully dried by exposure to solid muriate ol lime, their
volume, after firing, will not be at all condensed, and muriatic
acid gas, precisely equal to their joint bulk, will be obtained.
422 CHLORINE WITH HYDROGEN. CHAP. XIV.
By weighty one part of hydrogen gas requires 33.5 of chlorine
gas for saturation, and 34.5 of muriatic acid gas are produced.
The result of this experiment may either be explained, by
admitting the direct combination of hydrogen and chlorine to
constitute muriatic add; or by supposing that the hydrogen
unites with the oxygen of the oxy- muriatic acid, and that the
water, thus formed, exists as an element of muriatic acid gas.
In this instance, the theory of chlorine has certainly the ad-
vantage in point of simplicity.
If the weight of the atom of chlorine be determined from
its union with hydrogen, it will be expressed by 33.5 ; and
33.5 of chlorine will be the equivalent to 7.5 of oxygen.
When oxygen is made the decimal unit, as by Dr. Wollaston,
the weight of the atom of chlorine will be expressed by 44.1,
or in round numbers by 44. On the supposition that the
oxy-muriatic acid is a compound of muriatic acid and oxygen,
it must be constituted as follows :
Oxygen . 22.65 .... 100. .... 29.28
Muriatic acid ... . 77.35 .... 341.5 .... 100.
. — ■ ■ ■ . . ■— » ' ■ '• ' » '
100. 441.5 129.28
This would indicate the weight of the atom of muriatic acid
to be nearly 26 ; and adding an atom of oxygen, the compound
atom of oxy-muriatic acid would still weigh 33.5.
A remarkable fact, respecting the mutual action of oxy-
muriatic acid and hydrogen gases, was discovered by Gay
Lussac, and, without any knowledge of his experiments, by
Mr. Dalton. A mixture of the two gases, in equal volumes,
is slowly condensed under ordinary circumstances; but if the
direct rays of the sun happen to fall on the mixture, the two
gases diminish with considerable rapidity ; and, if the quan¬
tity be large, they even explode. This is a striking instance
of the agency of light in promoting chemical union. Blue
light is more effective in producing the condensation than red,
but neither occasions the rapid combustion, which is excited
by the direct rays of the sun *. It is probable, that in this
case, the combination is favoured by increase of temperature,
* Seebeck, 34 Nicholson’s Journal, p. 220.
SECT. I.
MURIATIC ACID GAS.
423
which was ascertained by Sir H. Davy to augment the com-
bustibility of mixtures of oxygen and hydrogen gases. Ac¬
cording to Grotthus, a mixture of chlorine and hydrogen
ceases to explode by electricity when rarefied six times, but
Sir H. Davy found it to be still explosive when rarefied no
less than 24 times.
Muriatic Acid Gas and its Solution in Water ;
I. The muriatic acid, in its purest form, exists in the state
of a gas, which is permanent over mercury only. For exhibit¬
ing its properties, therefore, a mercurial apparatus is absolutely
necessary.
To obtain muriatic acid gas by a more easy method than
the direct union of chlorine and hydrogen gases, let the tubu¬
lated gas bottle (plate ii. fig. 17) be about one fourth, or one
third, filled wfith well dried muriate of soda (common salt) in
lumps, not in powder. To this adapt the acid-holder, filled
with concentrated sulphuric acid ; and let the aperture of the
bent pipe terminate under a jar filled with, and inverted in,
quicksilver. Open the communication between the acid and
the salt, by turning the cock ; and immediately on the contact
of these two bodies, an immense quantity of muriatic acid gas
will be disengaged. A common or tubulated gas bottle, or
tubulated retort, will answer sufficiently well for procuring the
gas. The first portions, that come over, may be allowed to
escape under a chimney; because they are contaminated by
the admixture of common air present in the bottle. The sub-
sequent portions may be preserved for use ; and the pure gas
will exhibit the following qualities :
(a) It has a very pungent smell; and is sufficiently caustic
to blister the skin, when applied to it for some time.
(b) When brought into contact with common air, it occa¬
sions a white cloud. This is owing to its union with aqueous
vapour, which is always present in the atmosphere.
(c) It extinguishes a lighted candle. Before the flame goes
out, the upper part of it assumes a greenish hue, the cause of
which has not yet been explained. A white vapour also sur¬
rounds the extinguished wick, owing to the combination of
424
MURIATIC ACID GAS
CHAP. XIV.
water, produced by the combustion of the candle, with the
muriatic acid gas.
(d) It is heavier than common air. Gay Lussac states its
specific gravity at 1/278, and hence 100 cubic inches weigh, as
nearly as possible, 39 grains ; according to Sir H. Davy be¬
tween 39 and 40. Biot and Arago make its specific gravity,
by experiment, 1.2474, or, by calculation, 1.2505.
(e) It effects the liquefaction of a piece of ice, almost as ra¬
pidly as it would be melted by a red-hot iron*
(f) It is very rapidly absorbed by water. A drop or two
of water, admitted to a large jar full of this gas, causes the
whole of it instantly to disappear. According to Mr. Kir-
wan, an ounce-measure troy of water absorbs 800 cubical
inches {i. e. 421 times its bulk) of muriatic acid gas; and the
water, by this absorption, is increased about one third its ori¬
ginal volume. Dr. Thomson’s experiments indicate a still
larger absoi ption, viz. 515 cubical inches, or 308 grains by
one cubic inch, equal to 252 grains, of water, at 60° Fahren¬
heit ; the baromeU r standing at 29.4. Berthollet has shown
that 100 grains of water absorb 12 467 grains of muriatic acid
gas deprived of all redundant water by passing it through a
tube surrounded by a freezing mixture. By this absorption,
we obtain an acid of the specific gravity 1061.4 ; and hence it
follows that acid of this density contains, in 100 grains, only
8.55 of real acid.
(g) When potassium is introduced into muriatic acid gas,
dried by contact with fused muriate of lime, it immediately
becomes covered with a white crust; it heats spontaneously ;
and, by the assistance of a I mp, acquires, in some parts, the
temperature of ignition, but does not inflame. If the potas¬
sium and the gas be in proper proportions, they both entirely
disappear; a whi e salt is formed, and a quantity of pure hy¬
drogen gas is evolved, which is equal to rather more than one
third the original volume of the acid gas. Eight grains of
potassium, in an experiment of Sir H. Davy, effected the ab¬
sorption of nearly twenty-two cubic inches of muriatic acid
gas : and the quantity of hydrogen gas produced amounted to
P4pre than eight cubical inches. It is remarkable that potas-
SECT. I.
MURIATIC ACID GAS.
425
slum, by its action on muriatic acid gas, separates exactly the
same quantity of hydrogen, as would result from its agency
on water. This has been considered as a proof, that the
evolved hydrogen has its origin from water, which the gas is
supposed to hold in combination. But the phenomena are
equally well explained by admitting, that muriatic acid is de¬
composed by the potassium, which seizes the chlorine, and sets
the hydrogen at liberty. And on the corpuscular theory of
Mr. Dalton, whether potassium act on water or on muriatic
acid, in each case an atom of hydrogen will be disengaged ;
since the metal must attract to itself either an atom of oxygen
or of chlorine.
Various expedients were tried, by Sir H. Davy, to obtain
muriatic gas from perfectly dry materials, with the view to
determine, whether potassium is capable of detaching hydro¬
gen from gas so prepared. But it was found that materials,
which when moist are capable of affording muriatic acid, yield
no gas whatsoever, when in a perfectly dry state. None, for
example, could be obtained by strongly heating a mixture of
dry phosphoric or boracic acid with dry muriate of lime.
This fact would appear, on first view, favourable to the opinion,
that water is essential to the constitution of muriatic acid gas.
But it is equally consistent with the theory of chlorine; for,
according to that theory, no compound of chlorine and a me¬
tallic base can yield muriatic acid, till hydrogen is supplied
with which the chlorine may unite. If muriatic acid gas con¬
tained water as an essential element, it might be expected that
water should be separated by the action of certain metals on
the gas itself, or on muriate of ammonia ; and though experi¬
ments in proof of this have been advanced by Dr. Murray
and Dr. Ure *, yet, on repeating those experiments, sources
of fallacy have been discovered by Sir H. Davy, which had
escaped their authors ; and the moisture has been traced to
the union of oxygen derived from unsuspected sources with
the hydrogen of the muriatic acid f .
( h ) When muriatic acid gas is electrified in contact only
^ r.- ■ - - ■ ■ - — — — - - — . — ‘
# Edin. Trans.
t Phil. Trans. 1818, p. 169.
-126
MURIATIC ACID GAS.
CHAP. XITf
with glass, by means of an apparatus which I have described
in the Phil. Trans, for 1812, chlorine and hydrogen gases are
found, after the experiment, in quantity never exceeding ^th
the original bulk ot the gas. This result may either be ex¬
plained by supposing that the water of muriatic acid gas is
decomposed, and that the oxygen unites with the acid, while
the hydrogen is liberated ; or it may be accounted for on the
new theory, which requires nothing more than the separation
of the chlorine and hydrogen, constituting muriatic acid, by
the agency of the electric fluid. They cannot, however, exist
together in a greater proportion than dj to the whole mixture,
without re-uniting and re-forming muriatic acid. When the
experiment is made over mercury, the chlorine combines with
that metal, and a mixture of muriatic acid and hydrogen gases
remains, from which water absorbs the former, leaving the
hydrogen pure.
(: z ) When muriatic acid gas and oxygen gases are electrified
together, oxymuriatic acid is formed, directly, as the old
theory would explain, by the union of the acid with oxygen ;
or, as the theory of chlorine teaches, the oxygen unites with
the hydrogen of muriatic acid gas, and merely liberates chlo¬
rine.
(k) Muriatic acid gas and nitrous acid have no action on
each other, and are incapable of forming aqua regia. But
when colourless nitric acid and muriatic gas dissolved by water
are brought into contact, the hydrogen of the muriatic acid,
according to Sir H. Davy, detaches the 0x3^011 of the nitric
acid, and the chlorine of the former acid is developed. On
the old theory, this fact may be explained by supposing the
attraction of muriatic acid insufficient to take oxygen from
nitrous acid; but that it has the power of attracting that quan¬
tity of oxygen which constitutes the difference between nitrous
and nitric acids. The former view, however, it must be ad¬
mitted, is the more simple and perspicuous.
(/) When a small piece of barytes or strontites, obtained
by the decomposition of the nitrate, and therefore free from
water, is heated by means of a spirit lamp, in a retort filled
with muriatic add gas, the gas is first dilated, and is then
1
SECT. r.
LIQUID MURIATIC ACID.
427
rapidly absorbed. The barytes or strontites becomes red-hot,,
and the compound, which is produced, runs into fusion *, At
the close of the experiment, a sensible quantity of water is
condensed. This water may either have pre-existed in the
muriatic acid gas, or it may have been formed, by the union
of the hydrogen of the acid, with the oxygen of the barytes
or strontites which has been employed. Under the latter view,
we are to consider the solid product as a compound of chlo¬
rine with barium or strontium.
Process for preparing Liquid Muriatic Acid .
Into a tubulated retort, placed in a sand-bath, put eight
parts of dried muriate of soda ; and, to the tubulure, lute the
bent tube (fig. 26, a) with fat lute. To the neck of the retort,
affix a tubulated receiver (fig. SO, b ) by means of the same
lute; and to the aperture of this adapt a tube, twice bent at
right angles, and furnished with Welter’s contrivance for pre¬
venting absorption (fig. SJ, 6), the longer leg of which ter¬
minates beneath the surface of water contained in a two-necked
bottle. From the other neck, let a second right-angled pipe
proceed ; and this may terminate in a similar manner, in a
second bottle containing water; the total quantity of which,
in all the bottles, may be about five parts. Let the junctures
be all carefully luted ; and, when they are sufficiently hardened,
pour very gradually through the bent tube five and a half
parts by weight of strong sulphuric acid, making the addi¬
tions at several distant intervals. On each affusion of the acid,
a large quantity of muriatic acid gas will be liberated, and
will be absorbed by the water of the first bottle, till this has
become saturated. It will then pass on to the second bottle,
and be there absorbed. The water employed may amount to
half the weight of the salt, and may be equally distributed
between the two bottles. These it is better to surround with
cold water, or, still preferably, with ice or snow ; because the
condensation of the gas evolves considerable heat, which pre¬
vents the water from attaining its full impregnation. When
the whole of the sulphuric acid has been added, and the gas
* Chevreul, 84 Ana. de China. 285.
LIQUID MURIATIC ACID,
CHAP. XIV.
428
no longer issues, let a fire be lighted in the furnace, beneath
the sand-bath, removing the bent tube a , and substituting a
well-ground glass stopper. This will renew the production of
gas ; and the temperature must be preserved, as long as gas
continues to be evolved. At this period it is necessary to keep
the luting, which connects the retort and receiver, perfectly
cool; otherwise it will be apt to melt. To this juncture, in¬
deed, I prefer the application of the clay and sand lute ; but
to apply this properly requires a little practice. Towards the
close of the process, a dark-coloured liquid is condensed in
the first receiver, consisting of a mixture of sulphuric and mu¬
riatic acids. When nothing more comes over, the operation
may be suspended, and the liquid in the two bottles must be
preserved in bottles with ground stoppers. It consists of liquid
muriatic acid.
The liquid muriatic acid may also be obtained by diluting
the sulphuric acid with the water necessary for the condensa¬
tion of the gas, and adding the dilute acid, wrhen cold, to the
salt in the retort. To the retort, an adopter may be luted
with the clay and sand lute; and this may terminate in a large
tubulated receiver, from the aperture of which a right-angled
Welter’s tube is conveyed beneath a few ounces of water, con¬
tained in a two-necked bottle. A fire must then be lighted
under the sand-bath, and continued as long as any liquid
comes over. The adopter and receiver must be kept cool, by
the constant application of moistened cloths.
The proportions, directed by the London College of Phy¬
sicians, in their Pharmacopoeia of 1809, are those recom¬
mended by Vauquelin, viz. four parts of dried salt, three of
sulphuric acid, and three of water, of which last one third is
to be employed in diluting the acid, and two thirds to be put
into the receiver. Mr. R. Phillips, however, finds that the
water and acid are in unnecessary excess; and that the most
economical proportions are 32 parts of salt, and 21.9 (say 22)
of sulphuric acid, of density 1.850, which may be diluted
with one- third its weight of water, the remaining two thirds
being placed, as before, in the receiver *. The weight of the
* On the London Pharmacop. p. 10.
SECT. L IigCID MURIATIC ACID. 429
acid produced should equal, or a little exceed, that of the salt
employed.
If the muriatic acid, thus obtained, should contain sulphuric
acid, which may be discovered by muriate of barytes occa¬
sioning a white precipitate, the acid is to be re-distilled from
a fresh portion of muriate of soda. When prepared by
Woulfe’s apparatus, the product in the second bottle is always
perfectly pure.
The acid, formed by the process of the College, has the
specific gravity only of about 1.142; that of commerce is
generally about 1.156; but by Woulfe’s apparatus, and espe¬
cially when the bottles are surrounded by ice or snow, it ap¬
proaches 1.500. A fluid ounce of the specific gravity 1.142
dissolves 204 grains of marble ; and the same quantity of sp.
gr. 1.174 decomposes 240 grains. The intermediate degree
of specific gravity, however, which has been mentioned (viz.
1.156 or thereabouts), is best adapted for keeping; for the
denser acid emits a large quantity of fumes, which are ex¬
tremely inconvenient and injurious to all metallic instruments.
The caput mortuum consists of sulphate of soda with some
tindecomposed muriate of soda. The former may be obtained,
in a crystallized form, by first driving off, by a strong heat,
the excess of sulphuric acid that adheres to it ; and then dis¬
solving it in hot water. The product of sulphate of soda ex¬
ceeds that of the muriate employed in the proportion of about
eight to five.
Liquid muriatic acid has the following properties :
1 . It emits white suffocating fumes. These consist of mu¬
riatic acid gas, which becomes visible by contact with the
moisture of the air.
2. When heated in a retort, or gas bottle, muriatic acid
gas is disengaged, and may be collected over mercury.
3. Liquid muriatic acid is not decomposed by the contact
of charcoal, essential oils, or other combustible bodies.
4. When diluted with water, an elevation of temperature is
produced, much less remarkable, however, than that occa¬
sioned by diluting sulphuric acid ; and when the mixture has
cooled to its former temperature, a diminution of volume is
found to have ensued. The capacity of the diluted acid for
430
LIQUID MURIATIC ACID
CHAP. XIY*
heat Dr. Ure has found to be less than the mean capacity of
the strong acid and of water, which sufficiently accounts for
the increased temperature #.
5. In a perfectly pure state liquid muriatic acid is quite
colourless ; but it has frequently a yellowish hue. This may
proceed, either from a portion of chlorine, or of muriate of
iron, but most commonly of the latter. This colour is in¬
stantly destroyed by a few drops of muriate of tin ; but this
addition, instead of diminishing, increases the impurity of the
acid.
6. Muriatic acid combines readily with alkalies, and with
most of the earths, both in their pure and carbonated states.
7. Liquid muriatic acid is specifically heavier than water.
The correspondence between its specific gravity, and the
quantity of real acid, wffiich it contains, is shown by the fol¬
lowing Table, given by Sir H. Davy in his Elements of Che¬
mical Philosophy. It is constructed from experiments made
with great care by Mr. E. Davy in the Laboratory of the
Royal Institution.
Table showing the Quantity of real Acid in Liquid Muriatic
Acid of different Specific Gravities. (Temp. 45° Baht,
Barorn. 30.)
Specific
Gravity.
100 grains contain of
Muriatic Acid Gas.
Specific
Gravity.
100 Grains contains of
Muriatic Acid Gas.
1.21
42.43
1.10
20.20
1.20
40.80
1.09
18.18
1.19
38.38
1.08
16.16
1.18
36.36
1.07
14.14
1.17
34.34
1.06
12.12
1.16
32.32
1.05
10.10
1.15
30.30
1.04
8.08
1.14
28.28
1.03
6.06
1.13
26.26
1.02
4.04
1.12
24.24
1.01
2.02
1.11
22.3-
The proportion of dry or real muriatic acid, in liquid acid
* Thomson's Annals, x. 273.
S' EOT. II*
CHLORINE WITH OXYGEN,
431
of different densities, has also been investigated by Dr. lire,
who has ascertained that acid of density 1.192 contains in 100
parts by weight 28.3 of real muriatic acid ; and has given
some general formulae for deducing the proportion of real
acid in liquid acid of various specific gravities The table,
deduced from his experiments, will be found in the Appendix
at the end of the second volume.
SECTION II.
Compound of Chlorine with Oxygen , viz. Oxides of Chlorine ;
Chloric Acid , and Per-chloric Acid.
When chlorate or hyper-oxymuriate of potash (a salt
which will be afterwards described) is distilled, at a gentle
heat, with weak muriatic acid, a gas may be collected over
mercury, which is found to differ essentially from chlorine.
Its colour has a dense tint of brilliant yellow green ; and its
smell resembles that of burnt sugar, mixed with the peculiar
smell of chlorine. W ater seems to take up eight or ten times
its volume, and acquires an orange tint. It has been called
by its discoverer, Sir. H. Davy, Euchloric gas? or simply
Euchlorine . Gay Lussac has proposed for it the name of oxide
of chlorine ; but it may, with more propriety, be called Prot¬
oxide of Chlorine .
Euchlorine explodes by a gentle heat, applied to the vessel
which contains it, and five parts in volume become six, con¬
sisting of a mixture of oxygen and chlorine gases, in such
proportions that euchlorine must be composed of two in vo¬
lume of chlorine and one of oxygen, the latter being con¬
densed into half its bulk, or by weight of
Chlorine ........ 81 .44 ........ 1 00.
Oxygen ........ 18.56 ........ 22.79.
100.
These proportions indicate that euchlorine is constituted of
* Thomson’s Annals, x. 369 ,
432 CHLORINE WITH OXYGEN. CHAP. XIV.
one atom of chloline 33.5 4- one atom of oxygen 7.5* and
hence its atom must weigh 41.
When detonated with twice its volume of hydrogen gas*
there is a condensation of more than twro thirds of the mix¬
ture, and liquid muriatic acid is formed.
Mercury has no action on euchlorine at common tempe¬
ratures. Antimony and copper burn in it, if introduced
previously heated. Sulphur and phosphorus decompose it ;
and charcoal already ignited burns in it with a dull red light.
Nitrous gas condenses it with red fumes.
Euchlorine destroys vegetable colours ; but it first gives the
blue a tint of red.
In almost all cases of vivid combustion, there is a conden¬
sation of the bodies which unite ; but in the decomposition of
euchlorine by heat, we have the remarkable phenomenon of
an explosion, accompanied writh heat and light, and an ex¬
pansion of the elements, which are separated from each other.
Per-oxide of Chlorine .
Another compound of chlorine and oxygen, containing a
larger proportion than euchlorine, of the latter element, has
been discovered by Sir H. Davy*, and has since been made
the subject of a series of experiments by Count Stadion of
Vienna f. As it exhibits no acid properties, it may be called
per-oxide of chlorine.
To procure it, 50 or 60 grains of the powdered chlorate or
hyper-oxy muriate of potash, are to be mixed with a small
quantity of concentrated sulphuric acid. When thoroughly
incorporated, a solid mass will result, of a bright orange
colour. This is to be introduced into a small retort of glass,
which is to be exposed to the heat of water gradually warmed,
but prevented from attaining the boiling point, by an admix¬
ture of spirit of wine. Count Stadion obtained it by fusing
a small quantity of chlorate (hyper-oxymuriate) of potash, in
a retort. Over this, when cool, he poured concentrated sul¬
phuric acid, and exposed the retort to water for three hours,
* Phil. Trans. 1815, Part II.
f Thomson’s Annals, ix. 22,
SECT. II.
CHLORINE WITH OXYGEN.
433
gradually raising its temperature to 212°. The gas may be
received over mercury, on which it has no action at common
temperatures.
It has a lively yellow colour, much more brilliant than that
of euchlorine ; is much more rapidly absorbed by water ; and
has a peculiar aromatic smell, not mixed with any smell of
chlorine. According to Davy, it destroys vegetable blue
colours, without first reddening them ; but Count Stadion
asserts that it does not change blue paper. When heated to
about the temperature of 212° Faht., or, according to Count
Stadion, to between 112° and 144°, it explodes with more
violence, and a greater expansion of volume, than euchlorine,
producing much light. After explosion over mercury, from
2.7 to 2.9 volumes appear, for every two of gas decomposed ;
and, of these, two, as Count Stadion, also, admits, are oxy¬
gen and the rest chlorine. A little chlorine is absorbed, how¬
ever, by the mercury, and it is reasonable, Sir H. Davy
thinks, to conclude that the deep yellow gas is, in reality,
composed of two in volume of oxygen, and one of chlorine,
condensed into two volumes. If this be correct, the gas will
consist, by weight, of one atom of chlorine 33.5, and four
atoms of oxygen 30, and its atom will weigh 63.5. But if, as
Stadion asserts, it gives two volumes of chlorine and three of
oxygen, it should consist of one atom of chlorine and only
three of oxygen.
It is decomposed, at common temperatures, by no com¬
bustible body, except phosphorus, which occasions an explo¬
sion when introduced into it, and burns, in the liberated
gases, with great brilliancy.
Its saturated solution in water, which contains seven vo¬
lumes of gas, is of a deep yellow colour. It does not taste
sour, but extremely astringent and corroding ; and it leaves
on the tongue a disagreeable and lasting impression. The
solution may be kept in the dark unchanged, but when ex¬
posed to the sun’s rays it is decomposed, and chlorine and
chloric acid are obtained.
Chloric Acid.
A third compound of chlorine and oxygen was pointed out
vol. i. 2 F
434 CHLORINE WITH OXYGEN* CHAP. XIV.
by Mr. Chenevix, some time before it was obtained in a sepa¬
rate form, as existing in the class of salts called hyper-oxy-
muriates. For the method of exhibiting it in a distinct state*
we are indebted to Vauquelin # and Gay Lussac. f The fol¬
lowing is the process : To a solution of pure chlorate of ba¬
rytes (the mode of preparing which will be described in
art. 4. sect. 4), add by degrees dilute sulphuric acid, as long
as it occasions any precipitation. This separates the barytes*
and leaves the chloric acid combined with water only. It is
important to add no more sulphuric acid than is barely suffi¬
cient ; for the slightest excess renders the chloric acid impure.
If the right quantity has been used, the liquid obtained should
remain perfectly transparent, when, taking two separate por¬
tions of it, we add to the one dilute sulphuric acid, and to
the other chlorate of barytes. If either of these agents occa¬
sions a precipitate, we must add it by degrees till the effect
ceases. The clear liquid is then to be decanted by a syphon,
and reserved for use. It is a solution of chloric acid in water ;
and has the following properties.
1. It is free from colour ; its taste is acid and astringent;
and its smell, when concentrated and a little heated, is mode¬
rately pungent.
2. It reddens the infusion of litmus. Paper stained with
litmus, though it does not immediately lose its colour, yet is
deprived of it in a day or two if left in the liquid ; or more
rapidly if taken out of the liquid and exposed to the air, in
consequence of the solution becoming more concentrated.
3. It does not precipitate either silver, mercury, or lead,
from their solution in nitric acid.
4. It is volatilized by heat, but not without a partial de¬
composition into chlorine and oxygen. Hence it afterwards
precipitates the nitrate of silver.
5. Muriatic acid decomposes it, and both acids, if mixed
in just proportion, are changed entirely into chlorine. On
the old theory, part of the oxygen of the chloric acid passes
to the muriatic acid, and oxygenates it. On the new theory
of chlorine, the oxygen of the chloric acid unites with the
* Ann. de Chim. xcv. 10*3.
f Ibid. xci. Ill*
SECT. II.
CHLORINE WITH OXYGEN.
435
hydrogen of the muriatic acid, and the chlorine, pre-existing
in both, is thus developed.
6. Chloric acid is decomposed, also, by sulphureted hy¬
drogen and by sulphurous acid. In the first case, chlorine
and sulphur are separated, and water is formed. In the
second, sulphuric acid is formed, and chlorine set at liberty.
None of the acids, which are saturated with oxygen have any
action on chloric acid.
7. All the metals that are capable of decomposing water,
decompose also the chloric acid, and afford compounds of
chlorine with a metallic oxide.
According to the experiments of Vauqueiin, chloric acid
is composed of
Chlorine ........ 35 ..... . 100 ...... 54
Oxygen ........ 65...... 185...... 100
100.
This determination differs materially from that of Gay
Lussac, according to whom 32.304 oxygen convert 28.924
chlorine into chloric acid, and hence it should be composed
of
Chlorine . . . 47.3 ...... 100 ...... 90
Oxygen ........ 52.7 ...... 110,...., 100
100.
The result of Gay Lussac is by much the more probable of
the two, and would make the chloric acid consist of 1 atom
of chlorine + 5 atoms of oxygen, while Vauquelin’s numbers
would indicate no less than 8 atoms of oxygen. Mr. Che-
nevix formerly stated the composition of the hyper-oxymuriatic
or chloric acid to be 65 oxygen + 35 muriatic acid. To ac¬
commodate this view to the new theory, 10.4 taken from the
oxygen and added to the muriatic acid will give 45.4 and
54.6, numbers not very different from those of Gay Lussac.
It is proper, however, to add that the existence of a simple
combination of chlorine and oxygen has been denied by Sir
H. Davy, who considers the liquid, obtained by Gay Lussac*
2 f 2
436 CHLORINE WITH OXYGEN, CHAP. XIV*
as constituted of two proportions (atoms) of hydrogen, one of
chlorine, and six of oxygen. To this, the latter has replied,
that the hydrogen is not an element of the acid itself, but of
water with which the acid is united, as is the case with liquid
sulphuric and nitric acids. The reader, who takes an interest
in this controversy, may find it in the first volume of Annales
de Chimie et de Physique, and of the Journal of Science and
the Arts ; and the argument for the existence of hydrogen in
certain acids as an essential and acidifying principle, and not
as a constituent of water, has, also, been ably supported by
Dr. Murray, in a late volume of the Edinburgh Transactions.
Per-chloric Acid.
In obtaining peroxide of chlorine by Sir H. Davy’s, or by
Count Stadion’s process, a peculiar salt is formed, which was
first noticed by the latter philosopher. It is mixed with bi¬
sulphate of potash, which may be separated by a second crys¬
tallization, and the peculiar salt then appears in octohedral
crystals. It requires 55 times its weight of water at 60° for
solution, but dissolves freely in boiling water. In alcohol it
is quite insoluble. When distilled with an equal weight of
sulphuric acid, at a temperature of 280° Faht. it is decom¬
posed : and an acid (of whose properties, however, we have
not a distinct account) may be distilled over. When the salt
is distilled alone at 412°, it is converted into chloride of potas¬
sium (dry muriate of potash) and oxygen gas, in the follow¬
ing proportions. One hundred parts by weight afford
Muriate of potash .... 54.08 containing ^25*59 chlorine111
Oxygen . . 45.92
100.
Hence it appears that 25.59 chlorine are united with 45.92
oxygen, which is nearly in the proportion of 33.5 chlorine to
58 oxygen. Now to have agreed with the proportion of seven
atoms of oxygen, the last mentioned number should have been
52.5 ; and if we suppose the oxygen a little over-rated, which
may very probably be the case in a compound so imperfectly
SECT. III.
CHLORINE WITH NITROGEN,
437
investigated, the per-chloric acid will then consist of one atom
of chlorine = 33.5, united with seven atoms of oxygen ==
52.5 ; and the weight of its atom will be 86.
SECTION III.
Chlorine with Nitrogen .
Chlorine has no action whatsoever on nitrogen gas, noi
on nitrous gas or nitrous oxide, when both gases are perfectly
dry ; but a compound of chlorine and nitrogen may be formed,
by passing chlorine gas through a solution of nitrate of am*
monia, or of almost any ammoniacal salt, of the temperature
of 40° to 50° Fahrenheit. The chlorine gas is rapidly ab¬
sorbed, and a film appears on the surface, which soon collects
into yellowish drops, that sink to the bottom of the liquor.
This yellowish and oily fluid is the most powerfully deto¬
nating compound with which we are acquainted. When
gently warmed, it explodes with so much violence, that it is
not safe to employ a quantity larger than a grain of mustard
seed. Its discoverer, M. Dulong *, was severely wounded in
his first experiments on this substance ; and Sir H. Davy had
a serious injury done to his eyes in repeating them. It is ex¬
pedient, therefore, to proceed with great caution.
When a globule of this fluid is thrown into olive oil, tur¬
pentine, or naphtha, it explodes even without heat, and so
violently, as to shatter any glass vessel. The same effect
ensues, when it touches phosphorus, or phosphorized alcohol
or ether ; but pure alcohol seems to deprive it of its explosive
property, and renders it a white oily matter.
The specific gravity of the fluid, Sir H. Davy has deter¬
mined to be 1.653, water being 1. It is not congealed, by ex¬
posure to the cold produced by snow and muriate of lime.
The products of its detonation are chlorine and nitrogen
gases, but it is impossible to determine the bulk of those ele¬
ments which are afforded by a given weight. The best method
* See Ann. de Chun, voL 85,
6
438
CHLORINE WITH METALS*
CHAP. XIV.
of analyzing it, is by its action on mercury, which unites with
the chlorine, and sets the nitrogen free. From various ex¬
periments of this kind, Sir H. Davy concludes that it is com¬
posed of four in volume of chlorine to one in volume of nitro¬
gen, or of
Chlorine . 91.2
Nitrogen . 8.8
100.
These proportions correspond best with the opinion, that
it is constituted of one atom of nitrogen to two atoms of chlo¬
rine: but the coincidence is not so exact, as in the case of
some other compounds, and the analysis requires confirmation*
Chlorine and nitrous gases, separately dried by solid mu¬
riate of lime, do not combine on admixture ; but when mois¬
ture is present, the chlorine decomposes water, forming mu¬
riatic acid with its hydrogen, while its oxygen condenses the
nitrous gas.
SECTION IV.
Chlorine with the Metals of the Alkalies and Earths , and with
the Oxides of those Metals .
When potassium is heated in chlorine gas, it burns much
more vividly than in oxygen; each grain absorbs 1.1 cubic
inch of the gas, and a neutral compound is formed, precisely
resembling that which results from heating potassium in dry
muriatic acid gas. Sodium burns in chlorine with similar
appearances, and condenses twice as much of the gas, as is
absorbed by an equal weight of potassium.
When potassium or sodium, which have been made to ab¬
sorb oxygen, are heated in chlorine gas, the latter disappears,
and oxygen gas, precisely equivalent to what had been con¬
densed, is liberated. Oxygen is expelled, also, by chlorine,
from barytes, strontites, and lime, in the proportion of one
measure for every two measures of chlorine that are condensed.
As the oxygen is always evolved in its original quantity,
though the quantity of chlorine absorbed is variable, Sir H.
2
SECT. V. CHLORINE WITH CHARCOAL, &C. 439
Davy considers this as proving that the oxygen does not pro¬
ceed from the chlorine, but from the oxide ; and that chlorine
is a simple body, which attracts the metals in question more
strongly than oxygen attracts them.
Ammonia is decomposed by chlorine, sometimes with de¬
tonation. If both gases are dry, no water is produced, which
Sir H. Davy observes should happen, if chlorine contained
oxygen ; but the products are muriatic acid (from the union
of the chlorine and hydrogen), and nitrogen gas *. The mu¬
riatic acid, with the undecomposed alkali, forms muriate of
ammonia,
SECTION V.
Chlorine with Charcoal , Carbonic Oxide , and Carbureted Hy¬
drogen, .
When the charcoal of beech wood, finely powdered and
perfectly dry, is poured into chlorine gas in its ordinary state,
an inflammation ensues. But charcoal, intensely ignited by
the strongest powers of Voltaic electricity, in dry chlorine gas,
effects no change, nor is any carbonic acid produced f.
Perfectly dry chlorine and light carbureted hydrogen gases,
in the experiments of Dr. John Davy, detonated without pro¬
ducing carbonic acid. Muriatic acid gas was formed, and the
charcoal was precipitated. But when the gases are fired over
water, carbonic acid is obtained, the oxygen for which is fur¬
nished by the water. Mixtures of three or four parts of
chlorine and one part of carbureted hydrogen over water,
when exposed to the light of the sun, explode, and carbonic
acid is generated ; or, if the quantities are small, and indirect
light only is admitted, the action of the gases goes on slowly,
with similar results. -
When three measures of chlorine are mixed with two and
a half of olefiant gas or per-carbureted hydrogen , a white cloud
appears, and, if the gases are pure, the whole is rapidly con¬
densed. At the same time, a liquid resembling oil is formed,
* Phil. Trans. 1814, p. 70.
f Children, Phih Trans. 1815, p. 369.
MO CHLORINE WITH CHARCOAL, &C. CHAP. XIV.
which has a greater specific gravity than water. From this
property, per-carbureted hydrogen first received the name of
olefiant gas ; but it has been lately show'n that the liquid ob¬
tained is analogous, not to oil but to ether, whence it has
been called chloric ether . It will be described under that name
in the second volume.
The condensation of per-carbureted hydrogen by chlorine
gas affords an easy way of estimating the quantity of the
former, in any mixture of it with hydrogen, light carbureted
hydrogen, and carbonic oxide gases. Add to any gas, sus¬
pected to contain olefiant gas, about half its bulk of chlorine;
if an immediate diminution ensue, accompanied with an evi¬
dent production of an oily liquid, the presence of olefiant gas
may be safely inferred. Of the whole quantity condensed,
about 45 hundredths may be estimated to be per-carbureted
hydrogen.
A mixture of equal volumes of chlorine and carbonic oxide
gases, both dried by fused muriate of lime, and exposed,
about a quarter of an hour, to bright sunshine, affords a pecu¬
liar compound, called by its discoverer, Dr. John Davy *,
Phosgene Gas. The colour of the chlorine is destroyed by
this combination, and the constituent gases are condensed into
half their bulk. Hence it appears to be one of the heaviest
gases known, 100 cubic inches being estimated to weigh
105.97 grains.
Phosgene gas has an intolerably pungent odour, and red¬
dens litmus, whence it is called by some chemists phosgenic
acid. Water changes it into muriatic and carbonic acid gases.
The metals decompose it, and unite with the chlorine, a vo¬
lume of carbonic oxide being liberated, equal to the bulk of
the original gas. It condenses four times its volume of am-
moniacal gas, and the product is a white neutral salt, from
which the stronger acids disengage muriatic and carbonic
acids ; but acetic acid dissolves it without effervescence.
*
Phil. Trans. 1812.
SECT. VI.
CHLORINE WITH SULPHUR.
Ml
SECTION VI.
Chlorine with Sulphur and its Compounds .
Sulphur, when heated in contact with chlorine gas, ab¬
sorbs it, and forms a singular compound first described by
Dr. Thomson Ten grains absorb nearly 30 cubic inches
of gas, which is nearly in the proportion of 15 (the weight of
an atom of sulphur) to 33.5 (the weight of an atom of chlo¬
rine). It appears, indeed, to be a true chloride of sulphur.
This fluid is volatile below 200° Fahrenheit. Its colour is
red by reflected light, but yellowish green by transmitted
light. It emits fumes, which are peculiarly acrid, and which
excite a copious flow of tears. Its specific gravity is 1.6. It
decomposes water, the hydrogen of which forms, with the
chlorine, muriatic acid ; while the sulphur, with the oxygen
of the water, composes sulphuric acid. Before dilution, how¬
ever, it is not acid, and does not redden dry litmus paper.
Dry chlorine gas has no action on dry sulphurous acid gas;
but if water be present, muriatic and sulphuric acids result
from their mixture.
When chlorine gas is mixed with sulphureted hydrogen gas,
the phenomena vary with the proportions. When equal bulks
are used, there is scarcely any condensation, and the residue
contains -i^-fhs of its bulk of muriatic acid gas. In this case
sulphur is precipitated. But if enough of chlorine be used,
besides the same product of muriatic acid, the sulphur is
changed into chloride of sulphur.
The compound of chlorine and phosphorus will be de¬
scribed in speaking of the latter substance.
SECTION VII.
Chlorine with the Metals,
Almost every metal, in a state of minute division, takes
* Nicholson’s Journal, 8vo, voh vi
4 42
NOMENCLATURE.
CHAP. XIV.
fire spontaneously, and burns in this gas. The very malleable
metals, such as gold, silver, &c. which can be reduced to ex¬
tremely thin leaves, are best applied to the gas in that state.
Others, as iron, zinc, copper, &c. must be introduced in the
state of fine filings. The most readily oxidized metals burn
with the greatest brilliancy. The best proportion is about 40
grains of each metal to 40 cubic inches of gas : and, into the
bottom of the receiver a little sand may be poured, to prevent
it from being broken.
Metallic antimony burns with a very brilliant white flame,
and throws out sparks. Arsenic exhibits a fine green or blue
flame, attended with sparks, and a dense white smoke ; bis¬
muth a bluish flame ; nickel, a yellowish white one ; cobalt, a
bluish white ; zinc, a white flame and sparks ; tin, a bluish
white light ; lead, a clear white flame ; copper, a red and
slowly spreading light ; and iron, a bright red light. In all
these experiments, the temperature of the gas should not fall
short of 70°.
When chlorine is made to act on any metallic oxide, those
of iron and arsenic excepted, the whole of the oxygen is ex¬
pelled from the oxide, and the chlorine combines with the
metal only. The description of these compounds, which have
been ably investigated by Dr. J. Davy, will form a part of
the history of the individual metals in the next volume.
Nomenclature of the Compounds of Chlorine and of Muriatic Acid .
The combinations of muriatic acid continue to be termed
Muriates in the modified nomenclature, proposed by Sir H.
Davy. Thus muriate of magnesia, of alumine, and of am¬
monia, are correct expressions. But all compounds of chlo¬
rine with combustible bases, that philosopher proposes to de¬
signate by annexing the termination ane to the Latin name of
the basis. The compound of chlorine and sulphur, he calls
for example, sulphur ane ; that of silver ( argentum ) and chlo¬
rine ar gent ane ; and so of the rest. Common salt, on the
same principle, would be termed sodane. When these com¬
pounds are capable of uniting with an additional proportion
of chlorine, he expresses that which has two proportions by
the termination ana or anea . Thus copper ( cuprum ) with one
SECT. VII.
NOMENCLATURE.
443
proportion of chlorine is cupreine , and with two cupranea. This
nomenclature appears, however, to have gained little accepta¬
tion among chemists.
It is more agreeable to analogy with the combinations of
oxygen, to distinguish the compounds of chlorine by the name
of chloride , a termination conformable to that of oxide. The
different compounds of chlorine with one base, may then be
designated in the way proposed by Dr. Thomson for the
oxides, the first being called proto-chloride , the second deuto-
chloride , and so of the rest. Gay Lussac, conceiving chlorine
to have a stronger analogy with sulphur and phosphorus than
with oxygen, proposes for its compounds the name of chlo-
rures ; but, as it appears to me, without sufficient reason.
It will assist the recollection of the reader, if a general view
be now offered of the various compounds of chloride, and of
their nomenclature.
I. With Hydrogen, chlorine forms only one compound,
muriatic acidy for which the name of hydro-chlore or hydro¬
chloric acid has been proposed by the French chemists. For
its compounds, they propose, instead of muriates , the epithet
hydro-chlorates .
II. With Oxygen, it composes four compounds :
With one atom of chlorine to one of oxygen, protoxide of
chlorine , ( euchlorine of Davy).
With one atom of chlorine to four of oxygen, peroxide of
chlorine .
With one atom of chlorine to five of oxygen, chloric acid '.
With one atom of chlorine to seven of oxygen, perchloric
acid .
III. With Combustible and Metallic Bases:
With Carbon . . No combination.
- - — Carbonic oxide . . Phosgene gas.
■ - Nitrogen. ...... Chloride of nitrogen (Detonating
compound of Dulong).
. - Sulphur . Chloride of Sulphur (Fuming
Phosphorus
liquor of Thomson).
Protochloride of phosphorus.
Perchloride of phosphorus.
• • * •
MURIATES.
CHAP. XIV.
444
With Metals
{1. Protochlorides.
2. Deuto-chlorides.
3. Trito-chlorides.
4. Tetro-chlorides.
According to the views of Sir H. Davy and Gay Lussac,
all the bodies described in the next section, excepting the
muriates of ammonia, magnesia, and alumine, are to be con¬
sidered strictly as chlorides or chlorures, that is to say, as com¬
pounds of chlorine with metallic bases. Common salt, for
example, they conceive to be a compound, not of muriatic
acid and soda, but of chlorine and sodium, at least in its dry
state. Until these views, however, are completely established,
I have deemed it unnecessary to separate bodies, so naturally
allied by similarity of properties ; and I shall continue, there¬
fore, to class with the muriates, some compounds, which, in
the farther progress of science, will probably be removed to
a different genus of salts.
SECTION VIII.
Muriates ( Hydro- Chlorates).
Art. 1. — Muriate of Potash.
Muriate of potash may be obtained by saturating muriatic
acid with carbonate of potash, and evaporating the solution
till the salt crystallizes. These crystals have a cubical shape,
and a bitter disagreeable taste ; they dissolve in three times
their weight of water at 60°, and in a rather less proportion
of boiling water. They undergo little change when exposed
to the air ; they decrepitate when thrown on the fire, but
abandon no part of their acid at a red heat.
Muriate of potash consists, in 100 grains,
According to Berthollet . of . .
- , — — - — Berzelius ..... . — . .
■ . . . — Dr. Wollaston. . — . .
Acid.
33.34 ..
36.742..
36.57 ..
Base.
66.66
63.258
63.43
• t
SECT. VIII.
MURIATES OF POTASH AFJD SODA.
445
Berzelius, by decomposing 100 grains of the fused salt with
solution of nitrate of silver, obtained 192.4 of luna cornea.
According to Sir H. Davy, this salt after fusion is composed
of 75 parts of potassium united with 67 chlorine, or 100 grains
consist of
Potassium . . . . 52.8
Chlorine , .......... 47.2
100.
These proportions are almost the same as those stated by
Gay Lussac, viz. 100 chlorine + 111.31 potassium, all con¬
firming that this salt is composed of an atom of each of its
ingredients. A hundred parts, it is calculated by Dr. Ure,
when completely decomposed by sulphuric acid, yield 1294- of
liquid muriatic acid, specific gravity, 1.192.
Art. 2 . — Muriate of Soda .
Muriate of soda is that well known substance, common salt,
which is become a necessary ingredient in the food of man,
and is of essential utility in several of the arts.
I. Its composition may be proved, by the direct union of
soda with muriatic acid. But for purposes of experiment, the
common salt may be employed, which is to be found in the
shops. This may be purified, by adding to a solution of it
in water a solution of carbonate of soda, as long as any milk¬
iness ensues ; filtering the solution, and evaporating it till it
crystallizes.
II. Its qualities are as follow :
1. It crystallizes in regular cubes, which, when the salt is
pure, are but little changed by exposure to the air. The com¬
mon salt of the shops, however, acquires an increase of weight,
in consequence of the absorption of moisture. The various
forms under which it appears, of stoved salt, fishery salt, bay
salt, &c. arise rather from modifications in the size and com¬
pactness of the grain, than from any essential difference of
chemical composition.
2. It requires, for solution, twice and a half its weight of
water, at 60° of Fahrenheit, and hot water takes up very lit-
446
MURIATES.
CHAP. XIV.
tie more. Hence its solution crystallizes, not like that of nitre,
by cooling, but by evaporation.
3. When heated gradually it fuses, and forms, wheh cold,
a solid compact mass.
4. If suddenly heated, as by throwing it on red-hot coals, it
decrepitates. It does not, however, after being dried at the
temperature of boiling water, lose by ignition more than two
or three parts of water per cent, and essentially it contains no
water.
5. It is not decomposed when ignited in contact with in¬
flammable substances, except with potassium, which sets at
liberty half its weight of sodium.
6. When mixed with powdered charcoal or sulphur, and
fused in a crucible, it does not undergo any decomposition or
essential change.
7. It is decomposed by the carbonate of potash, the alkali
of which combines with the muriatic acid of the salt, and the
carbonic acid is transferred to the soda. — Hence we obtain
muriate of potash and carbonate of soda. A process for
effecting this decomposition, on a large scale, is described by
Westrumb, in Crelfs Journal, English translation, ii. 127.
8. It is decomposed by the sulphuric acid in the mode al¬
ready described. Nitric acid also separates the muriatic acid.
9. Muriate of soda is composed, in 100 grains,
Acid. Base.
According to Darcet .... of _ 49.27 . . 50.73
• — . . . * Berard . . . . — ... .43. . . 57.
- - - - Dr. Marcet — . . . .46. . . 54.
- — . . Berzelius . . . . .46.55 . . 53.44
From 100 grains of transparent rock salt, dissolved in water,
and precipitated by nitrate of silver, I obtained 242 of luna
cornea ; Dr. Marcet, from 100 grains of pure artificial muriate
of soda, fused before solution, obtained 241.6; Berzelius,
244.6; and Rose, 243.4. Now 100 grains of luna cornea
may be stated, in round numbers, to denote 19 grains of real
muriatic acid, so that it is easy, from this datum, to calculate
the composition of common salt, or of any muriatic salt, which
has been decomposed by nitrate of silver.
SECT. VI IE
MURIATE OF AMMONIA.
447
On the atomic system of Mr. Dalton, it should consist of
an atom of muriatic acid combined with an atom of soda. But
according to Sir H. Davy’s view, fused common salt is con¬
stituted of an atom of sodium, weighing 22, with an atom of
chlorine weighing 33.5, or of
Sodium . . . . .
. 40.5 . . .
... 100 ...
Chlorine . . . .
. 59 5 . . .
. .. 147 .. .
... 100
100.
247
168
Dr. Wollaston assumes its constitution to be either 39.64
sodium + 60.36 chlorine; or, on the old theory of muriatic
acid, he admits its composition as stated by Berzelius. One
hundred grains are estimated by Dr. Ure to be capable of
yielding, when completely decomposed by sulphuric acid, 165
of liquid muriatic acid, specific gravity 1.190, or 186.3 grains
of density 1.160.
Art. 3 Muriate of Ammonia .
1. If equal measures of ammoniacal gas and muriatic acid
gas be mixed together, over mercury, they are immediately
and totally condensed, a white cloud is formed, and a solid
substance is deposited on the sides of the vessel. — -This is the
muriate of ammonia. For experimental purposes it may be
procured in the shops, under the name of sal-ammoniac.
Berzelius, from 100 grains, precipitated by nitrate of silver,
obtained 267.87 of luna cornea. Hence he calculates its
composition, independently of water, to be
Acid ........ 60.8 _ 100.
Ammonia .... 39.2 ........ 64.48
100.
But in its ordinary state the salt contains water, for when
distilled with lime, the earth gains a greater increase of weight
than the muriatic acid only could furnish. The proportions
are, according to Berzelius,
448 MURIATES. CHAP. XIV,
Acid . 49.55
Base . . 31.95
Water . . . ] 8.50
100.
These proportions differ very little from the results of Dr.
Ure, who infers the dry muriatic acid in 100 parts of sal-am¬
moniac to be 50 or 51 only *, equivalent to 67.8 of the acid
gas-
This is one of the few salts, which, consistently with Sir H.
Davy’s views, can properly be considered as a true muriate.
Its atomic constitution Mr. Dalton believes to be one atom of
acid and two atoms of ammonia. The notion of its being a
compound of chlorine with the imaginary substance of am¬
monium, or a chloride of ammonium , appears not to be te¬
nable f .
Muriate of ammonia exhibits the following properties :
(a) It is volatilized, without being liquefied or decomposed,
or in other words may be sublimed. Sir IT. Davy finds that
it may even be passed, without alteration, through glass or
porcelain tubes heated to redness. When, however, it is
transmitted over ignited metals, it is decomposed into its gas¬
eous elements.
(b) It is readily soluble in water, three parts and a half of
which, at 60° take up one of the salt. During its solution
much caloric is absorbed. In boiling water, it is still more
soluble ; and the solution, on cooling, shoots into regular
crystals.
(c) It slightly attracts moisture from the air.
(d) On the addition of a solution of pure potash, or pure
soda, the alkali is disengaged, as is evinced by the pungent
smell that arises on the mixture of these two bodies, though
perfectly inodorous when separate.
(e) Though generally considered as a neutral salt, yet, if
placed on litmus paper and moistened, Berzelius observes,
that the paper is reddened after some moments, as it would be
by an acid.
f Ure in Thomson’s Annals, x. 211.
✓
* Thomson’s Annals, x. 211.
SECT. VIII. MURIATES OF AMMONIA AND EARYTES. 419
(/) It is decomposed by barytes, strontites, lime, and
magnesia.
Process for obtaining Solution of Ammonia in water .
The following process is given by Mr. R. Phillips, as pre¬
ferable to that of the London Pharmacopoeia *.
On 9 oz. of well-burnt lime, pour half a pint of water,
and when it has remained in a well closed vessel for nearly an
hour, add 12 ounces of muriate of ammonia, and about 3-E
pints of boiling water. When the mixture has cooled, filter
the solution ; and, having put it into a retort, distil off 20
fluid ounces. The solution will have the specific gravity-
0.954, which is quite as strong as it can be conveniently kept.
If the solution be required to be more strongly impregnated,
this will be best effected, by passing ammoniacal gas through
it, from a mixture of equal parts of powdered lime and mu¬
riate of ammonia, by means of an apparatus similar to that
described for the preparation of muriatic acid.
When a mixture of one part of powdered muriate of ammo¬
nia with from one to two of powdered carbonate of lime
(chalk), both perfectly free from moisture, is distilled together
in a retort, a solid white substance condenses on the inner
surface of the receiver. This is the sub-carbonate of ammo¬
nia ; and the process now described is that by which, with the
substitution of proper subliming vessels, the sub-carbonate of
ammonia is prepared for sale. This operation furnishes an
example of double affinity. The carbonic acid, being trans¬
ferred from the lime to the ammonia, forms sub-carbonate of
ammonia ; and the muriatic acid, passing to the lime, com¬
poses muriate of lime.
Art. 4 .—Muriate of Barytes .
Muriate of barytes may be formed by heating pure barytes
in chlorine gas, each measure of which disengages half a mea¬
sure of oxygen gas from that earth. Or when barytes is heated
in muriatic acid gas, the gas disappears, and the salt, which
is produced, becomes red hot. But lor purposes of expevi-
YOL, i.
* Remarks oft the London Pharm. p. 34.
2 G
450
MURIATES
CHAP. XIV.
nienfc, muriate of barytes is best prepared, by dissolving either
the artificial or native carbonate in muriatic acid much di¬
luted ; or, if neither of these can be had, the sulphuret. The
Iron and lead, which are occasionally present in the carbonate,
and are dissolved, along with the barytes, may be separated
by the addition of a small quantity of liquid ammonia, or by
boiling and stirring the solution in contact with a little lime ;
or, which is still better, by solution of barytes in water. When
filtered and evaporated, the solution yields regular crystals,
which have most commonly the shape of tables, bevelled at
the edges, or of eight-sided pyramids, applied base to base*
They dissolve in five parts of water, at 60°, or in a still
smaller quantity of boiling water ; and also in alcohol. They
are not altered by exposure to the atmosphere ; nor are they
decomposed, except partially, by a high temperature. The
sulphuric acid separates the muriatic ; and the salt is also de¬
composed by alkaline carbonates and sulphates.
Fifty grains of ignited muriate of barytes give 63 of luna
cornea. It is composed.
Acid. Base.
According to Mr. A. Aikin . . of .... 26.86 • . 73.14
. . . . Berzelius ..... . — .... 26.23 • . 73.77
And the crystallized salt consists
Acid. Base. Water.
According to Mr. Aikin, ..of 22.93 . . 62.47 . . 14.6
- Berzelius .... — 23.35 .. 61.85 .. 14.80
Its atomic constitution, according to Mr. Dalton, is 1 atom
of acid and 1 atom of base ; and the crystals consist of 1 atom
of dry salt and 2 atoms of water. Sir H, Davy considers the
dry salt as a compound of 1 atom of barium weighing 65, and
I atom of chlorine 33.5. Hence 100 parts should consist of
Chlorine . . . 34.
Barium . . 66.
100.
Art. 5. — Muriate of $ trout lies
May be obtained by following the same process as that em-
SECT. VIII. MURIATES OF STRONTITES AND LIME. 451
ploj^ed in preparing the barytic salt. The solution affords
long slender hexagonal prisms, which are soluble in two parts
of water, at 60°; and to almost any amount in boiling water.
In a very moist atmosphere they deliquiate. They dissolve in
alcohol, and give a blood-red colour to its flame.
Fifty grains of dry muriate of strontites give 85 of Juna
cornea, and hence the salt must consist of 67.5 base and 32.5
acid. This agrees very nearly with Kirwan’s determination, but
differs somewhat from Vauquelin’s, viz. 61 base and 39 acid.
Stromeyer, who has lately examined this salt, makes it consist
of
Base ........ 65.585 . . or . . 100.
Acid ....... 34.43 5 . . — .. 52.474
100.
According to Sir H. Davy's view, it is constituted of 2$
parts strontium and 21 chlorine, or of
Strontium . . . . 58.
Chlorine . . ...» 42.
Its atomic constitution, agreeably to this view, is one atom
of metal weighing 45, and one atom of chlorine weighing 33.5.
On the old theory, it should consist of one atom of strontites^
and one atom of muriatic acid.
Art. 6. — Muriate of Lime ,
This salt may be prepared by dissolving carbonate of lime
in muriatic acid, or by washing off the soluble part of the
mass which remains after the distillation of the solution of
pure ammonia from muriate of ammonia and lime. One hun¬
dred grains of carbonate give, according to Berzelius, 109.6
of fused muriate of lime.
The solution crystallizes in six-sided striated prisms, ter¬
minated by very sharp pyramids. If it be evaporated to the
consistence of a syrup, and exposed to a temperature of 32 9
It forms a compact mass, composed of bundles of needle-
shaped crystals, crossing each other confusedly. The dry
salt retains its acid at the temperature of ignition «
2 G 2
452
MURIATES.
CHAP. XIV.
The crystals dissolve in half their weight of cold water, and
to an unlimited extent in boiling water, being, in fact, soluble
in their water of crystallization.* — They deliquiate rapidly in the
air, and enter into fusion when heated. After being melted
by a strong heat, the fused mass still contains water ; for by
ignition with iron filings, it yields much hydrogen gas. On
the new theory of chlorine, however, this gas may proceed
from the decomposition of muriatic acid. If fused in a cruci¬
ble, and treated in the same manner as the nitrate of lime,
the crystals yield a solar phosphorus, called, from its disco¬
verer, Homberg’s phosphorus . When mingled with snow, they
produce intense cold, as has already been described.
Dry muriate of lime may be inferred, from an experiment
of Dr. Marcet, to consist of
Muriatic acid ............ 49 . 100
Lime . . . 51 ...... 104
100.
One hundred grains of fused muriate of lime give, accord¬
ing to Davy, 250 grains of luna cornea ; according to Berze¬
lius 287.5. From experiments on its synthesis, Berzelius
states its composition to be
Add .............. 48.54
Lime ............ 51.46
100.
and that of the crystallized salt
Acid 24.69
Lime . 25.71
Water ............ 49.60
100.
But, according to the theory of Sir H. Davy, the salt after
being ignited, consists of 31 chlorine and 19 calcium, or of
Chlorine ...... 62 . 100 .... 163
Calcium ...... 38 . 61 .... 100
100,
SECT. VIII. MURIATES OF MAGNESIA, ALUMINE, &C.
453
Art. 7.-- -Muriate of Magnesia,
This is also a deliquescent and difficultly crystallised salt.
It has an intensely bitter taste ; is soluble in its own weight
of water, or in five parts of alcohol. Unlike the preceding
muriates, it is decomposed, but not entirely, by ignition.
According to Mr. Dalton, muriate of magnesia is consti¬
tuted of 56.4 acid + 43.6 base; but from Dr. Wollaston’s
table of equivalents, it may be deduced to consist of 58 acid
and 42 base. The compound of chlorine and magnesium,
though supposed by Sir H. Davy to exist, has not yet been
examined in a separate state. When heated, the combina¬
tion, he remarks, is destroyed ; the chlorine decomposes water,
and escapes in the state of muriatic acid, and the oxygen of
the water forms magnesia with the metal.
The muriates of magnesia and lime are generally contained
in muriate of soda, and impart to that salt much of its deli¬
quescent property. They impair, too, its power of preserving
food. They are also ingredients of sea-water.
e
Art, 8. — Muriate of Alumine
May be formed by dissolving fresh precipitated alumine in
muriatic acid ; but the acid is always in excess. It is scarcely
possible to obtain this salt in crystals ; for, by evaporation, it
assumes the state of a thick jelly. It is extremely soluble in
water, and deliquescent when dry. In a high temperature it
abandons its acid entirely. No compound (Sir H. Davy ob¬
serves) exists, that can be considered as a compound of alu*
mine and chlorine.
Art. 9. — Muriate of Glucine ,
This salt is little known. Like all the salts of glucine, it
has a sweet taste, and crystallizes more readily than the nitrate.
Art. 10. — Muriate of Zircon,
Fresh precipitated zircon is readily dissolved by muriatic
CHLORATES.
CHAP. XIV
acid. The compound is colourless ; has an astringent taste ;
and furnishes, by evaporation, small needle-shaped crystals,
which lose their transparency in the air. It is very soluble in
water and in alcohol. It is decomposed by heat, and by the
saliva of the mouth. The gallic acid, poured into the solu¬
tion, precipitates, if it be free from iron, a white powder.
Carbonate of ammonia gives a precipitate, which is re-dis¬
solved by an excess of the carbonate.
Art. 11 ,—Muriate of Yttna,
This compound has a striking resemblance to nitrate of
yttria. Like that salt it dries with difficulty, and attracts
moisture from the air. It does not crystallize, when evapo^
rated, but forms a jelly.
SECTION IX,
Chlorates or Hyper-oxy -muriates.
Art. 1 Chlorate or Hyper-oxy -muriate of Potash
The properties of this salt were discovered by Berthollet, -
It may be formed either by the direct mixture of liquid chlo-
rine acid with solution of potash or carbonate of potash -or
by passing chlorine gas, as it proceeds from the mixture of
muriate of soda, sulphuric acid, and manganese (see Sect. II,
Process 2), through a solution of caustic potash. This may
be done by means of W oulfe’s apparatus, using only one three¬
necked bottle in addition to the balloon. The tube, which is
immersed in the alkaline solution, should be at least half an
inch in diameter, to prevent its being choked up by any
crystals that may form. The solution, when saturated with
the gas, may be gently evaporated, and the first products
only of crystals are to be reserved for use ; for the subsequent
products consist of common muriate of potash only.
The chemical changes that occur in the production of chlo¬
rate of potash may be explained either on the old or the new
theory. Let us (on the old hypothesis) suppose the oxy-mu-
SECT. IX.
CHLORATE OF POTASH.
4 55
riatic acid, when first presented to the alkaline solution, to be
divided into two portions ; one of these gives up its excess of
oxygen to the other half, and returns to the state of common
muriatic acid, which, combining with the alkali, forms muriate
of potash.™ The other portion, therefore, is oxy-muriatic acid*
plus a certain quantity of oxygen; and this, uniting with ano«
ther portion of alkali, forms a salt, which Mr. Chenevix has
termed hyper-oxy-muriate. Strictly speaking, therefore, sim¬
ply oxygenized muriate of potash does not exist; for the
acid in this salt contains 65 per cent, of oxygen ; whereas the
oxy-muriatic acid must contain, if any oxygen be present in
it, only 22.65 per cent.
It would be equally consistent with the theory of chlorine*
either to suppose that the oxy-muriatic acid decomposes the
water of the alkaline solution, forming, with its hydrocrem
common muriatic acid, wdiile another portion of chlorine
unites with the oxygen thus set at liberty ; — or that the change
consists in the decomposition of potash, the oxygen of part of
which is transferred to another portion of alkali, while the
oxy-muriatic acid is partly expended in decomposing water
and forming muriate of potash, and partly in composing a
triple compound of chlorine, oxygen, and per-oxide of potas¬
sium. In this view, hyper-oxy-muriate of potash is con¬
stituted of 1 atom of potassium weighing 40.5, 1 atom of
oxy-muriatic acid = 33.5, and 6 atoms of oxygen = 45 ; or
100 parts consist of
Chlorine .
Potassium
Oxygen . .
100.
On the theory of Mr. Dalton, one atom of oxy-muriatic
acid weighing 29, deprives five surrounding atoms of the same
acid of their oxygen, and constitutes one atom of hyper-oxy-
muriatic acid = 64, which unites with an atom of potash = 42,
These numbers are not very remote from those deducible from
Mr. Chenevix’s analysis, according to whom this salt is com¬
posed of
456
CHLORATES.
CHAP. XIV.
Hyper-oxy-muriatic acid . 58.3
Potash . 39.2
Water . 2.5
100.
The water, however, is in too small proportion to be consi¬
dered as more than an accidental ingredient.
Even by the advocates of the simple nature of chlorine, two
different views have been taken of this class of salts. By Gay
Lussac, the chlorates are considered as compounds of chloric
acid with alkaline and earthy bases ; by Sir H. Davy, they
are regarded as triple compounds of one atom of chlorine,
one atom of metallic base, and six atoms of oxygen. But
chloric acid being, as is deducible from the experiments of
Gay Lussac, compounded of five atoms of oxygen with one
atom of chlorine ; there is no difference as to the facts, what-
t
ever there may be as to their explanation, This will appear
from the following comparative statement.
According to Davy, C 1 atom of metallic base
Hyper-oxy-muriates or < 1 atom of chlorine
chlorates consist of 6 atoms of oxygen.
, v , r 1 atom of base, f 1 atom metal
According to Gay \ . ,. r < , .
r Pi , J 1 consisting or i 1 atom oxygen.
Lussac, chlorates < , , ^ ,, > .. .
, \ 1 atom or chlo- \ 5 atoms oxygen
are composed ot / 1 7
r (. nc acid £ 1 atom chlorine.
It will easily be perceived, on examining these statements,
that the same properties of elements are assigned by both phi¬
losophers to the chlorates, and that the only difference is as
to the manner in which those elements are arranged.
The chlorate of potash has the following qualities :
(a) It has the form of shining hexaedral laminae, or rliom-
boidal plates.
(b) One part of the salt requires 17 of cold water for solu¬
tion, but five parts of hot water take up two of the salt.
(c) It is not decomposed by exposure to the direct rays of
the sun, either in a crystallized or dissolved state.
(d) When chlorate of potash is submitted to distillation in
a coated glass retort, it first fuses, and, on a farther increase of
temperature, yields oxygen gas of great purity. A hundred
grains of the salt afford 75 cubic inches of gas ( = about
2
SECT. IX.
CHLORATE OF POTASH.
457
grains of gas), containing not more than three per cent, of
nitrogen gas. Berzelius, from the same quantity, obtained a
much larger product of gas, viz. 39.15 grains = 112 or 114.
cubic inches *. And Gay Lussac found that 1 00 grains give
38.88 grains of oxygen, and 61.12 of muriate of potash, con¬
taining, he supposes, 28.93 chlorine and 32.19 potassium. The
residue of this distillation (consisting, according to the new
theory, of chlorine and potassium) Vauquelin asserts f is sen¬
sibly alkaline ; from whence it should appear that the capacity
of saturation is less in chlorine than in chloric acid.
(e) The chlorate of potash has no power of discharging ve¬
getable colours ; but the addition of a little sulphuric acid, by
setting chlorine at liberty, developes this property.
(f) The salt is decomposed by the stronger acids, as the
sulphuric and nitric acids. This may be proved by dropping
a few grains of the salt into a little concentrated sulphuric
acid. A strong smell will arise, and, if the quantities be suf¬
ficiently large, an explosion will ensue. The experiments
should, therefore, be attempted with great caution. When
this mixture is made at the bottom of a deep vessel, the vessel
is filled with euchlorine gas, which inflames sulphuric ether,
alcohol, or oil of turpentine, when poured into it ; and also
camphor, resin, tallow, elastic gum, &c. (Davy.)— By the ac¬
tion ot sulphuric acid, regulated as already described, pecu¬
liar gaseous compounds result.
Muriatic acid, as has already been stated, disengages chlo¬
rine, and the addition of a few grains of the salt to an ounce
measure of the acid, imparts to it the property of discharging
vegetable colours.
(g) Chlorate of potash exerts powerful effects on inflamma¬
ble bodies.
1. Rub two grains into powder in a mortar, and add one
grain of sulphur. Mix them very accurately, by gentle tri-
ture, and then, having collected the mixture to one part of
the mortar, press the pestle down upon it suddenly, and for¬
cibly. A loud detonation will ensue.— Or, if the mixed in-
* Ann, de Chim. et Phys. v. 1750
f Ann. de Chim. xcv. 101.
45$
CHLORATES.
CHAP. XI*.
gradients be wrapped in some strong paper, and then struck
with a hammer, a still louder report w'ill be produced.
2. Mix five grains of the salt with half the quantity of pow¬
dered charcoal in a similar manner. On triturating the mix¬
ture strongly, it will inflame, especially with the addition of a
grain or two of sulphur, but not with much noise.
3. Mix a small quantity of sugar with half its weight of the
salt, and on the mixture pour a little strong sulphuric acid
A sudden and vehement inflammation will be produced. This
experiment, as well as the following, requires caution.
4*. To one grain of the powdered salt, in a mortar, add
about half a grain of phosphorus. The phosphorus will deto¬
nate, on the gentlest triture, with a very loud report. The
hand should be covered with a glove in making this experi¬
ment, and care should be taken that the phosphorus, in an
inflamed state, does not fly into the eyes. — Phosphorus may
also be inflamed under the surface of water by means, of this
salt. Put into a wine glass, one part of phosphorus with two
of the salt ; fill it nearly with water, and pour in, by means
of a glass tube, reaching to the bottom, three or four parts of
sulphuric acid. The phosphorus takes fire, and burns vividly
under the water. This experiment requires caution, lest the
inflamed phosphorus should be thrown into the eyes. (Davy.)
Oil may also be thus inflamed on the surface of water, the ex¬
periment being made with the omission of the phosphorus,
and the substitution of a little olive or linseed oil.
5. Hyper-oxy-muriate of potash may be substituted for
nitre in the preparation of gunpowder, but the mixture of the
ingredients requires extreme circumspection. It may be pro¬
per also to state, that this salt should not be kept mixed with
sulphur in considerable quantity, such mixtures having been
known to detonate spontaneously.
* A mixture of this kind is the basis of the matches, now generally used
for the purpose of procuring instantaneous light. The bottle, into which
they are dipped, contains concentrated sulphuric acid, which is prevented
from escaping by a quantity of finely spun glass or the fibres of amianthus,
SECT. IX.
CHLORATES OT SODA AND AMMONIA.
459
Art. 2. —Chlorate of Soda.
This salt may be obtained, by following the process already
described, with the substitution of pure soda for potash ; or
by adding chloric acid to carbonate of soda, till the efferves¬
cence ceases. It is exceedingly difficult, however, to obtain
it pure, by the first process, because it nearly agrees in solu¬
bility, with the common muriate of soda; and the second me¬
thod is therefore preferable. It is soluble in three parts of
cold water, and in rather less of hot, and is slightly deliques¬
cent. It is soluble also in alcohol; but so also, according to
Mr. Chenevix, is the common muriate. It crystallizes in
cubes, or in rhomboids approaching the cube in form. In
the mouth it produces a sensation of cold, and a taste scarcely
to be discriminated from that of muriate of soda. In other
properties it agrees with the similar salt with base of potash.
Art. 3.— -Chlorate of Ammonia.
This salt cannot be procured by the direct union of chlorine
with pure ammonia, because these two bodies mutually de¬
compose each other ; as will appear from the following expe¬
riments :
1. Fill a pint receiver with chlorine gas ; and pour into it
half a drachm of the strongest solution of ammonia that can
be procured. A detonation will presently ensue.
2. Fill a four-ounce bottle with chlorine gas, and invert it in
a cup containing four ounce-measures of the solution of pure
ammonia. Presently the liquor will be absorbed, and a deto¬
nation will ensue, which will throw down the bottle, unless
firmly held by the hand. In the bottle there remains a portion
of nitrogen gas.
Though not capable, however, of being formed by the
direct action of chlorine on solution of ammonia, yet an hyper-
oxymuriate or chlorate of ammonia may be obtained by adding
liquid chloric acid to solution of carbonate of ammonia, till
the effervescence ceases. The solution must be evaporated by a
very gentle heat, on account of the volatility of the salt ; and
it is best to allow it to evaporate spontaneously at the tempera¬
ture of the atmosphere.
CHLORATES.
CHAP. XIV.
4 GO
The salt, thus obtained, has the shape of very fine needles.
Its taste is extremely pungent. When heated, it detonates
per se9 like nitrate of ammonia, but at a lower temperature,
and with a red flame. When decomposed by heat in close
vessels, a large quantity of chlorine is obtained, with a very
small proportion of oxygen and nitrogen, and also of hydro¬
gen and muriate of ammonia. Hence it appears that the
hydrogen of the volatile alkali is more disposed to unite with
the oxygen than with the chlorine contained in the chloric
acid
Art. 4. — Chlorates with Earthy Bases.
1. Chlorate of Barytes. — To prepare this salt, chlorine gas
must be received into a warm solution of barytes in water, till
the barytes is saturated. The solution is to be filtered, and
boiled with phosphate of silver, which decomposes the com¬
mon muriate of barytes, and at the same time composes two
insoluble salts, phosphate of barytes, and muriate of silver.
Vauquelin finds the addition of acetic acid recommended by
Chenevix, objectionable, and that the compounds of chloric
acid are liable, if acetic acid has been employed, to detonate
violently when heated. To judge when enough of the phos¬
phate of silver has been used, add to a portion of the filtered
liquor, a few drops of nitrate of silver, which, in that case,
ought not to disturb its transparency. If too much phosphate
of silver has been used, a drop or two of muriatic acid will
discover it, and, in that case, the cautious addition must be
made of some of the original solution, set apart for, the pur¬
pose, to which no phosphate of silver has been added. It is
from solution of chlorate of barytes, thus carefully prepared,
that chloric acid is obtained by the intervention of sulphuric
acid.
Chlorate of barytes has the form of four-sided prisms ; its
taste is pungent and austere ; it requires for solution about
four times its weight of water, at 50° Fahrenheit; and its so¬
lution, when pure, is not precipitated either by nitrate of
silver or muriatic acid. By a red heat, it loses 39 per cent..
* Vauquelin, Ann. de Chira. xcv, 97,
SECT. IX. CHLORATES OF STRONTITES AND LIME. 461
and the residue is alkaline. From a calculation, founded on
its decomposition by sulphuric acid, it appears to consist of
Barytes . . 46
Chloric acid 54
100
2. Chlorate of Strontltes may be obtained by the direct action
of chloric acid on carbonate of strontites. It is a deliquescent
salt, having an astringent taste, and communicating to the
flame of alcohol a fine purple tint.
3. Chlorate of Lime . — To the account of this salt, I think
it proper to premise, that considerable uncertainty appears to
me still to exist respecting its composition. It is even doubt¬
ful whether the substance, formed by exposing dry hydrate of
lime to chlorine gas, is any thing more than a compound of
that hydrate with chlorine.
This compound derives importance from its application to
the art of bleaching; for its solution in water, even when
there is no excess of chlorine, possesses bleaching properties ;
and produces whiteness in the unbleached part of goods, with¬
out destroying any delicate colours which they may contain.
The dry compound, formed from hydrate of lime and chlorine
gas, is extremely deliquescent; liquefies at a low heat; and is
soluble in alcohol. It produces much cold by solution, and
a sharp taste in the mouth. Its composition and properties
have been investigated by Mr. Dalton, in two memoirs pub¬
lished in the 1st and 2d volumes of Dr. Thomson’s Annals.
He finds that the dry salt is a compound of two atoms of
lime, one of acid, and six of water. By solution, one half
of the lime is deposited, and a compound of one atom of lime
and one of acid is dissolved by the water. The dry salt is
much impaired by being long kept. It contains per cent, ac¬
cording to Dalton,
Chlorine , .......
Lime . .
Water . . . * . <
. . . 38. 4
100-
462
NITRO-MUR IATIC ACID*
CHAP. XIV*
For an account of the remaining salts formed with chloric
acid, Mr. Chenevix’s paper in the Philosophical Transaction8
for 1802, and Vauquelin’s memoir in the 95th volume of An-
nales de Chimie, may be consulted*
SECTION X.
Nitro- Muriatic Acid.
This acid may be formed most comm odiously by mixing
two parts by weight of colourless nitric acid with one of liquid
muriatic acid. Proust employs only one of nitric to four of
muriatic acid. Though the acids are both perfectly pale, yet
the mixture becomes of a deep red colour, a brisk efferves¬
cence takes place, and pungent vapours of chlorine are
evolved.
Considerable light has been thrown on the nature of this
acid by the experiments of Sir H. Davy *, who has rendered
it probable that its peculiar properties are owing to a mutual
decomposition of the nitric and muriatic acids, the oxygen of
the former uniting with the hydrogen of the latter, in conse¬
quence of which water, chlorine, and nitrous acid, are the re-
suits. For every 101 parts in weight of real nitric acid (equiva¬
lent to 118 of hydro-nitric acid) which are decomposed, 67
parts of chlorine, he calculates, are produced. According to
this view, it is not correct to say that aqua regia oxidates gold
or platinum, since it merely causes their combination with
chlorine. By long continued and gentle heat, nitro-muriatic
acid may be entirely deprived of chlorine, and it then idses
its power of acting on gold and platinum.
The nitro-muriatic acid does not form, with alkaline or
other bases, a distinct genus of salts, entitled to the name of
nitro-muriates ; for, when combined with an alkali, or an
earth, the solution yields, on evaporation, a mixture of a mu¬
riate and a nitrate ; and metallic bodies dissolved in it yield
muriates only. The most remarkable property of nitro-mu-
f Journal of Science, &c. i. 67*
SECT. XI.
MUKIO-SULPHURIC ACID.
463
riatic acid (that of dissolving gold, from whence it has been
calied aqua regia) will be described in the chapter on that
metal.
SECTION XL
Mur io- Sulphuric Acid .
Muriatic acid gas is absorbed in considerable quantity by
sulphuric acid. The compound has a brown colour, and
when exposed to the air emits copious white fumes. It has
no particular uses.
By the action of a mixture of fuming muriatic acid on sul-
phuret of carbon, Berzelius obtained a solid white crystalline
body, resembling camphor, and possessing some remarkable
properties. Its analysis afforded
Muriatic acid .................. 48.74
Sulphurous acid ................ 29.63
Carbonic acid (and loss) .......... 21 .63
100.
It appears, therefore to consist of two atoms of muriatic
acid, one of sulphurous acid, and one of carbonic acid.
V
»
*
'
APPENDIX.
DESCRIPTION OF THE PLATES.
PLATE !.
h IG. 1. (a) A plain retort, the neck of which is shown in*
trodnced a proper length into the mouth of a plain receiver b»
The dotted lines at c show the receiver with the addition of a
tubulure, into which either a stopper, or bent glass tube, may
be occasionally fixed.
Fig. 2. A glass alembic ; a the body, and b the head,
which are ground so as to fit accurately, and may be separated
when necessary. The head b is so shaped, that any liquid,
which may be condensed, collects into a channel, and is car¬
ried by the pipe c into the receiver.
Fig. 3. A separator , for separating liquids of different
specific gravities. It is furnished with a ground stopper at a,
and a glass stop-cock at b. The vessel is filled with the liquids
that are to be separated (oil and water for example), which
are allowed to stand till the lighter has completely risen to the
top. The stopper a is then removed, and the cock b opened,
through which the heavier liquid descends ; the cock being
shut, as soon as the lighter one is about to flow out.
Fig. 4. A glass vessel, termed a mattrass , useful for effect¬
ing the solution of bodies, which require heat before they can
be dissolved, or long continued digestion, see vol. i. p. 10.
The upper extremity of the long neck generally remains cool,
and allows the vessel and its contents to be shaken occasionally.
Fig. 5. A glass bottle with a very thin bottom, and a pro¬
jecting ring round the neck for suspending it over a lamp®
These are useful for effecting solutions on a small scale.
O
Fig. 6. An apparatus contrived by Mr. Pepys, for ascer¬
taining the quantity of carbonic acid discharged from any sub -
vol, i. 2 H
466
DESCRIPTION OF THE PLATES.
stance by the addition of an acid . It consists of a bottle closed
by a ground stopper. This stopper is perforated, and forms
the lower part of a tube, which is twisted into the shape of a
still-worm. In this worm, any water that escapes along with
the gas, is condensed, and falls down again into the bottle.
The experiment is made precisely as described, vol. i. p. 301 :
and the loss of weight is determined at the close of the effer-
vescerice.
Fig. 7. Mr. Leslie’s differential thermometer described,
vol. i. p. 75.
Fig. 8. (a) An air thermometer , for ascertaining the tem¬
perature of liquids. It consists of a bottle, partly filled with
any coloured liquid, and partly with air, a glass tube of small
bore, open at both ends, being either cemented or hermeti¬
cally sealed into the bottle, so that its lower extremity may
nearly touch the bottom of the bottle. The expansion of the
included air, on the application of heat, drives the coloured
liquid up the tube, and to an extent which may be measured
by the application of a scale. The fig. b is another variety of
the same instrument, described vol. i. p. 74.
Fig. 9. The original air thermometer of Sanctorio ; see
vol. i. p. 74.
Fig. 10. A bent funnel for introducing liquids into retorts,
without soiling their necks.
Fig. 11. An adopter . The wider end admits the neck of
a retort ; and the narrower is passed into the mouth of a re¬
ceiver.
Fig. 12. A section of an evaporating dish of Wedgwood’s
ware. Under this figure, is a representation, without any
number attached to it, of a small prong with a wooden handle,
for holding an evaporating glass over a lamp.
Fig. 13. (a) A tubulated retort luted to ( b ) a quilled re-
ceiver , the pipe of which enters the neck of a bottle (c) sup¬
ported by a block of wood.
Fig, 14. Different forms of jars for precipitations, with lips
for conveniently decanting the fluid from the precipitate.
Fig. 15. A tube, blown in the middle into a ball, for
dropping liquids. The ball is filled by the action of the mouth
applied to the upper orifice, while the lower one is immersed
in the liquid. To the former the finger is then applied ;
DESCRIPTION OF THE PLATES,
467
and, on cautiously removing it, the liquid is expelled in
drops.
Fig. 16, A bottle for ascertaining the specific gravity of
liquids . When filled up to a mark in the neck, with distilled
water of a given temperature, it should hold 1000, 2000, or
any even number of grains. The quantity, which it is found
to contain, of any other liquid of the same temperature, shows
the specific gravity of the latter. For example, if it hold
1000 grains of water, and 1850 of sulphuric acid, the specific
gravity of the latter is to that of water as 1850 to 1000,
PLATE IL
Fig. 17. An apparatus for procuring gases, without the
possibility of their escaping into the room during the process,
a circumstance which is of considerable importance, when
the gas has an unpleasant smell or deleterious properties.
Suppose that sulphureted hydrogen gas is to be obtained from
sulphuret of iron and diluted sulphuric acid. The sulphuret
of iron, in coarse powder, is put into the body of the gas
bottle c, with a proper quantity of water. The acid holder a
is filled with diluted acid, the cock l being shut, and is then
fixed into the tubulure of the gas bottle, to which it is accu¬
rately adapted by grinding. The bent tube d being made to
terminate under a receiver filled with, and inverted in water,
the perforated cock l is gradually opened, in consequence of
which the acid descends into the gas bottle ; and acts on the
sulphuret of iron. If it be found necessary to renew the acid,
without disturbing the apparatus, this may be done as follows.
The cock b being shut, the stopper, which closes the acid
holder, may be removed, and fresh acid be poured in, through
the aperture. This may be repeated as often as is found
necessary. The acid holder may be advantageously adapted,
also, to a retort for certain distillations, such as that of
muriatic acid.
Fig. 18. A plain gas bottle with sigmoid tube, the end,
which is received into the bottle, having a ground stopper ac¬
curately fitted to the neck. For ordinary purposes (such as
obtaining hydrogen gas from diluted sulphuric acid and iron
filings) this apparatus answers perfectly well, and is much less
2 H 2
468
DESCRIPTION OF THE PLATES®
costly. It is frequently made with a tubulure and glass stopper*
and is then called a tubulated gas bottle.
Fig. 19. A gas funnel, useful in transferring any gas, from
a wide-mouthed vessel into a jar of narrower diameter, or into
a bottle. When employed for this purpose, it is held inverted,
as shown by the figure, the pipe being admitted into the aper¬
ture of the bottle or jar, which is filled with and inverted in
water, and the gas being made to pass into it in bubbles.
Fig. 20. Dr. Hope’s Eudiometer. The manner of using
it has already been described, vol. i. p. 152.
Fig. 21. A modification of Dr. Hope’s Eudiometer de¬
scribed, vol. i. p. 152, 153.
Fig. 22. A gas receiver, into the neck of which is cemented
a brass cap, with a female screw for receiving a stop-cock.
The vessel b is a glass flask, which may be made to communi¬
cate with the interior of the jar a, by opening the cock.
When the apparatus is used, it is necessary to employ two
stop-cocks, and not one only, as represented by the figure.
Supposing that the weight of any gas is to be ascertained, the
flask b is exhausted, by screwing it on the transfer of an air-
pump ; and, if great accuracy be required, it is proper to en¬
close a gage in the vessel. Let the flask be weighed when
exhausted ; then screw it upon the top of the receiver, con¬
taining the gas which is to be weighed ; and open the commu¬
nication, observing, by using a graduated jar, how much gas
has been admitted. Suppose this to be 50 cubic inches. By
weighing the flask again when full, we determine the weight
of 50 cubic inches of the gas under examination. The ex¬
periment should be made when the temperature of the room is
60°, and when the barometer stands at 29.8.
Fig. 23. A plain jar for receiving gases, with a ground
stopper.
Fig. 24. An eudiometer for trying the purity of a mixture
of gases containing oxygen gas, by means of nitrous gas. The
process has already been described, vol. i. p. 391, 392. The
instrument should be accompanied with a phial, holding, when
completely full, precisely a cubic inch.
Fig. 25. A wire stand, with a leaden foot, for the purpose
of raising, above the surface of water within a jar, any sub¬
stance which is to be exposed to the action of gas.
I
DESCRIPTION OF THE PLATES* 469
Fig. 25. (a) A bottle and tube for directing a small stream
or a few drops of water on any object.
Fig. 25. (b) A bottle with an elongated stopper, by means
of which a single drop of any liquid can be taken up, and
allowed to fall into any fluid under examination.
Fig. 26. An apparatus for showing that caloric exists in
gases in a latent form. The application of it has been already
described, vol. i. p. 128.
Fig. 27. An apparatus for drying precipitates by steam,
described, vol. i. p. 11.
Fig. 28. A graduated tube for ascertaining the strength of
acids and alkalies, see vol. ii. part ii.
Fig. 29, a and b. Tubes for exploding mixtures of hy¬
drogen and other inflammable gases with oxygen gas, com-
monly termed the Eudiometer of Volta; see vol. i. p, 157®
PLATE III.
Fig. 30, The common form of a Wouife’s apparatus. In
this figure the retort a is represented plain, but it is better to
employ a tubulated one. The use of this apparatus has al¬
ready been described, vol. i. p. 7.
Fig. 31. A modification of the apparatus, which has
been already described. In this figure, the mercurial trough
is shown with a jar standing inverted in it, for the purpose
of receiving any gas that may escape condensation by water*
Fig. 32. Mr. Pepys’s improvement of Wouife’s apparatus
described, vol. i. p, 8.
PLATE IV.
Figs. 33 and 34*. Cuthbertson’s apparatus, for exhibiting
the composition of water, with the substitution of gazometers
for the receivers originally employed by him. The apparatus
has been described, vol. i. p. 167, 168. Fig. 33 is an enlarged
view of the conical brass piece, which is cemented into the
bottom of the receiver, and through which the gases are
conveyed.
Fig. 35. A gazometer of the most simple and common
construction ; see vol. i, p. 1 22.
Fig. 36. A gas holder, described, vol. i. p. 122.
Fig, 37® A galvanic trough; see vol. L p. 187. Thetubt
470
DESCRIPTION OF THE PLATES.
b shows the arrangement for decomposing water. The upper
wire may be hermetically sealed into the tube, and the lower
one passed through a cork, which should have a small slit
cut in it, to allow the water to escape in drops as the gas is
produced.
Fig. 38. The manner in which a candle may be burned in
oxygen gas ; see vol. i. p. 137.
Fig. 39. The combustion of iron wire in oxygen gas.
Fif. 40. Apparatus for decomposing water over red-hot
iron or charcoal ; see vol. i. p. 171, 172.
Fig. 41. An apparatus for showing the diminution effected
in the volume of I^drogen and oxygen gases by their slow
combustion; see vol. i. p. 160.
Fig. 42. A very simple and cheap contrivance for freez¬
ing quicksilver by muriate of lime and snow. The outer
vessel of wood may be twelve and a half inches square, and
seven inches deep. It should have a wooden cover, rabbeted
in, and furnished with a handle. Within this is placed a tin
vessel b b, standing on feet which are one and a half inch
high, and having a projection at the top, half an inch broad,
and an inch deep, on which rests a shallow tin pan c c.
Within the second vessel is a third cl, made of untinned iron,
and supported by feet two inches high. This vessel is four
inches square, and is intended to contain the mercury. When
the apparatus is used, a mixture of muriate of lime and snow
is put into the outer vessel a a, so as completely to surround
the middle vessel b b. Into the latter, the vessel d, containing
the quicksilver to be frozen, previously cooled down by a
freezing mixture, is put ; and this is immediately surrounded
by a mixture of snow and muriate of lime, previously cooled
to 0° Fahrenheit, by an artificial mixture of snow and
common salt. The pan c c is also filled with these materials,
and the wooden cover is then put into its place. The vessels
are now left till the quicksilver is frozen. A more elegant,
but more expensive apparatus, by Mr. Pepys, intended for
the same purpose, is figured in an early volume of the Philo¬
sophical Magazine.
Fig. 43. A wire stand, consisting of an interior circle,
and three straight pieces of wire proceeding from it in the
same plane. Its use is noticed, vol. i. p. 139.
5
DESCRIPTION OF THE PLATES®
471
Fig. 44. Sir H. Davy’s apparatus for the analysis of soils
described in his paper, which is copied into the third part of
this work.
PLATE V®
Fig. 45. Pictet’s arrangement of an apparatus for show¬
ing the radiation of caloric, unaccompanied by light; see
vol. i. p. 83.
Fig. 46. An oval copper boiler, for exhibiting the most
important facts respecting latent caloric. The size of its dif¬
ferent parts (except the width, which is 4 inches) may be
learned from the scale affixed to the plate, which is abun¬
dantly sufficient to enable any intelligent workman to con¬
struct the apparatus. The collar joint and stuffing box, how¬
ever, it is indispensably necessary to describe, especially as
the former article of apparatus is generally constructed on a
bad plan.
Fig. 47 is a section upon a larger scale, of the collar joint
at b (fig. 46), made for the convenience of screwing together
long or crooked metal tubes, without turning them round :
a is a section of the end of one of the tubes, and b that of
the other which is to be attached to it ; c is a collar which
turns loose upon the shoulder of u, and screws upon b . By
screwing this collar upon b , the end e e of the tube a is
brought to press upon the part d d of the tube b , without
turning round either of those tubes. If upon d be laid a ring
of linen cloth soaked in boiled linseed oil, the joint, when
screwed up (if tolerably well made), will be impervious to
steam as well as to water or air. The projection at d is for
preserving the ring of cloth from being displaced, and for
guiding the ends of both tubes, so as to meet properly.
Fig. 48 is a section of a socket, for fixing the stem of a
thermometer into a boiler or a digester, where there is much
heat and pressure ; b is a socket fixed on the outside ol the
boiler or digester, having a hole through it large enough to
admit the bulb of the thermometer; a is a plug which screws
into b , having a hole through its centre large enough to admit
only the stem of the thermometer ; c c is a loose round plate,
concave on the upper side, having a hole through its centre
just sufficient also to admit the stem of the thermometer
472
DESCRIPTION OF THE PLATES.
When the instrument is to be inserted, the plug or, and the
plate c, must both be taken out of the socket. The bulb is
then passed through it. The plate c is next slipped over the
stem, and dropped into its place. Some flax, soaked in lin¬
seed-oil, must next be wrapped round the stem, so as nearly
to fill the socket. The plug a must then be screwed in, till
the flax be compressed so as to make the whole sufficiently
tight. The opposite surfaces of the plate c, and the plug a
are made concave, for the purpose of compressing the flax
round the stem of the thermometer.
PLATE VI.
Figs. 49, 50, 51. Sections of crucibles.
Fig. 52. A muffle; see vol. i. p. 4.
Fig. 53. Stands for raising the crucible above the bars of
the grate ; a one adapted to Mr. Aikin’s blast furnace ; b one
of the common form.
Fig. 54. A skittle-shaped crucible.
Fig. 55. Mr. Aikin’s portable blast furnace. It is corn-
posed of three parts, all made out of the common thin black-
lead melting pots, sold in London for the use of the gold¬
smiths. The lower piece c is the bottom of one of these pots,
cut off' so low as only to leave a cavity of about an inch, and
ground smooth above and below. The outside diameter over
the top is five and a half inches. The middle piece, or fire¬
place a , is a larger portion of a similar pot, with a cavity
about six inches deep, and measuring seven and a half inches
over the top, outside diameter, and perforated with six blast
holes at the bottom. These two pots are all that are essen¬
tially necessary to the furnace for most operations ; but when
it is wished to heap up fuel above the top of a crucible con¬
tained within, and especially to protect the eyes from the in¬
tolerable glare of the fire when in full heat, an upper pot b
is added, of the same dimensions as the middle one, and
with a large opening in the side, cut to allow the exit of the
smoke and flame. It has also an iron stem, with a wooden
handle (an old chisel answers the purpose very well) for re¬
moving it occasionally.
The bellows, which are double (d)> are firmly fixed, by
DESCRIPTION OF THE PLATES*
a little contrivance which will take off and on, to a heavy
stool, as represented in the plate ; and their handle should be
lengthened so as to make them work easier to the hand. To
increase their force on particular occasions, a plate of lead
may be firmly tied on the wood of the upper flap. The
nozzle is received into a hole in the pot c, which conducts the
blast into its cavity. From hence the air passes into the fire¬
place a , through six holes of the size of a large gimlet, drilled
at equal distances through the bottom of the pot ; and all
converging in an inward direction, so that if prolonged, they
would meet about the centre of the upper part of the fire.
Fig. 56 shows the distribution of these holes in the bottom.
The large central hole is intended to receive the stand a, fig.
53, which serves for supporting the crucible.
No luting is necessary in using this furnace, so that it may
be set up and taken down immediately. Coke or common
cinders, taken from the fire when the coal just ceases to blaze,
sifted from the dust, and broken into very small pieces, forms
the best fuel for higher heats. The fire may be kindled at
first by a few lighted cinders, and a small quantity of wood-
charcoal.
The heat which this little furnace will afford is so intense,
that its power was, at first, discovered accidentally by the
fusion of a thick piece of cast iron. The utmost heat pro¬
cured by it was 167° of Wedgwood’s pyrometer piece, which
was withdrawn from a Hessian crucible, when actually sink¬
ing down in a state of porcellanous fusion. A steady heat of
155° or 160° may be depended on if the fire be properly ma¬
naged, and the bellows worked with vigour
By a letter from Mr. Aikin, I have learned, also, a con¬
venient way of exhibiting, in a lecture, and performing at
other times, the process of cupellation, by means of this fur¬
nace. It consists in causing a portion of the blast to be di¬
verted from the fuel, and to pass through a crucible in which
the cupel is placed. This arrangement supplies air ; and the
whole may be seen by a sloping tube, run through the cover
of the crucible. Fig 57 shows the furnace when used for this
purpose; a a the furnace; b the perforated stopper for the
* See Philosophical Magazine, vol. xvii. p. lotv
474
DESCRIPTION OF THE PLATES*
central blast ; cc a portion of earthen tube, through which
the air passes, and is heated during this transit ; e a piece of
soft brick perforated to admit the earthen tube f, which may
be kept open for inspecting the process. No luting is re¬
quired, except to join f to e .
Fig. 58. Knight’s portable furnace*, composed of strong
iron plate lined with fire lute, the inside diameter six inches :
a shows the grate ; h the ash pit door ; d the door of the fire¬
place when used as a sand heat ; e e two holes opposite to each
other for transmitting a tube : g an opening for a retort neck,
when used for distilling with the naked fire.
Fig. 59. A different view of the same furnace; a the
grate ; c the register to the ash pit ; f a small door, with a
contrivance for supporting a muffle. The other letters cor¬
respond with the explanation of the preceding figure.
For this furnace the proper fuel, when it is used as a wind
furnace, is wood-charcoal, either alone, or with the admix¬
ture of a small proportion of coak. For distillation wuth a
sand heat, charcoal, with a little pit coal, may be employed.
PLATE VII.
Fig. 60 represents a fixed furnace, which I find very useful,
because it may either be employed as a wind furnace or for
distillation with a sand heat. Its total height outside is thirty-
three inches, and the outside square is eighteen inches, or
two bricks laid lengthwise. The thickness of the sides of the
furnace is the breadth of a brick, or four and a half inches;
but whenever there is room, it is better to make them nine
inches in thickness. From the top of the furnace to the
grate, which is moveable, and supported by two bearers, the
height is thirteen inches ; and at c is a double Rumford door ;
or in preference, a hole closed by a moveable earthen stopper,
for introducing fuel. The ash pit should have a register
door. The chimney is four inches wide by three high, and
may either be furnished with a damper or not. On the top
of the furnace a cast-iron ring is fixed, ten inches inside
diameter, three inches broad, and half an inch thick. It is
secured in its place by three iron pins, passing through three
* This furnace is also described in vol. i. p. 2, 3.
DESCRIPTION OF THE PLATES.
475
equidistant holes in the ring, and bent at the distance of nine
inches at a right angle. These serve the purpose of binding
the ring firmly into the brick-work. The sand pots are of
different sizes ; and a variety of them may be made to fit the
same ring, by varying the breadth of their rims, as shown
fig. 71. The brick should be cemented together, at least for
the inner half of their breadth, by loam, or by a mixture of
Stourbridge clay, with two or three parts sand, and a proper
quantity of water.
When this is used as a wind furnace, the opening in the
side is to be closed by its stopper ; or, if a Rumford door be
employed, it must be defended from the fuel by a fire tile.
The fuel (coke) is introduced at the top, which is occasionally
covered bv a fire tile. When distillation with a sand heat is
performed, the sand pot rests on the iron ring, and the fuel,
which may be common pit coal, is added through the opening
in the side. It may be proper to state, that, in order to re¬
ceive a sand pot of as large a size as possible, the upper
course of bricks should be bevelled within the furnace ; and
the width at the top may exceed a little that at the grate.
The best Stourbridge or Newcastle-on-Tyne fire-bricks are
necessary in constructing this and the following furnaces.
Fi&. 61 is a longitudinal section of a wind furnace, in¬
vented by Mr. Knight, with an additional chamber for
applying the waste heat to useful purposes: a the internal
cavity, which is square, for containing the fuel and the
crucible : h the flue passing into a hot chamber c ; an ap¬
pendage particularly useful for drying luted crucibles, or
bringing them to a proper temperature for the furnace ?
for roasting ores and various other purposes : d the flue con¬
necting it with the vertical chimney e; which, to produce a
strong heat, should never be less than thirty or forty feet high :
ff covers, consisting of twelve-inch Welsh tiles, with handles:
g the stoke hole, through which no more of the fire is seen
than what appears between the grate and the bearing bar h .
This space is left for the double purpose of raking the fire,
and occasionally taking out the bars : k the ash pit, which is
sunk below the level of the ground, and is covered, where it
projects at /, by an iron grating.
The best situation for this furnace, is an angle of the labo-
476
DESCRIPTION" OF THE PLATES*
ratory, the chimney being in the corner, as represented in the
sketch. By this arrangement, the operator is spared the dis¬
agreeable necessity of scorching his legs, by standing opposite
the stoke hole, while the backs of his legs are exposed to a
current of cold air rushing to the furnace.
Figs. 62 and 63 are different views of a furnace invented by
Mr. Knight, and convertible to various purposes.
The inside of this furnace is nine inches square, and sixteen
inches deep from the top to the grate. The face of the open¬
ing at g rises at an angle, which makes the back part five
inches higher than the front. This contrivance enables us
completely to cover a large retort with fuel, without obstruct¬
ing the passage of the air, and also relieves partly the weight
of the cover, when it requires to be moved. The walls of the
furnace are at least a brick and a half thick, and as much
more as local convenience will allow. By sinking the ash pit
below the level of the ground, at i, the height of the furnace
needs not exceed eighteen inches, which renders the manage¬
ment of the fuel much more easy, and subjects the face and
hands less to the action of the heat. The ash pit a, must be at
least eighteen inches deep, below the surface of the ground,
and more if convenient. It must have an opening, projecting
from it three or four feet, to be covered with boards, and with
an iron grating next the furnace. This preserves the legs of
the operator from the action of the fire.
The grate L is formed of separate bars, each of a triangular
shape, three fourths of an inch apart, and resting on twx>
bearers. In the front of the furnace, an iron bar is to be
placed to support the brick-work, and to leave an opening,
through which the bars may occasionally be drawn out, and
the fire raked and cleared of the slag. The chimney e is two
and a half inches from the top, and four and a half wide by two
and a half high.
To fit this furnace for occasional distillation with the naked
fire, an opening, d, fig. 62, is left on one side, which is filled
up, when not wanted, by five pieces of soft fire-brick, cut to a
proper shape, and secured by a clay lute. It is proper, also,
to be provided with other pieces, having arched openings for
transmitting the neck of a retort. One of these pieces may
have a round hole for occasionally transmitting a tube, and
DESCRIPTION OF THE PLATES®
477
a corresponding hole, h, fig. 63, must then be made in the
opposite side of the furnace, to be closed, when not wanted,
with a stopper.
Flos. 64 and 65 represent a sand heat, for containing flat
evaporating vessels ; the depth from back to front two feet ;
the width, agreeably to the scale, six feet. At the front is a rim
four inches deep, consisting of a piece of iron plate, which is
fastened at each end into the walk The floor or bottom, e e9
is formed of cast-iron plates, which rest upon each other in
corresponding rabbets. The advantage of several small plates,
over one large one, is the cheapness and facility, with which
they are replaced, if cracked by the heat, an accident of not
unfrequent occurrence. The joints are secured by a fire lute,
which effectually prevents the sand from falling through.
The fire place is shown by b; at the bottom it has a grate ten
inches long, by eight wide. The flame and smoke circulate
first through the flue c, and then through the returning flue^,
which conveys the smoke to the chimney g . In constructing
the flue beneath the grate, a row of bricks, set edgeways,
answers the purpose, and serves also to support the inner edge
of the plates.
It is adviseable to cover the sand heat with a sloping roof,
which may be formed of lath and plaster, and supported
by side walls. The lowest part of the roof may be foremost,
and about three feet above the edge of the iron plates. It is,
also, necessary to have an air flue, nearly at the top of the
back wall, under the dome or roof, to be closed occasionally by
a door. This must open into the chimney, in which case it
serves the purpose of carrying off1 noxious vapours.
PLATE VIII.
Figs. 66, 67, 68, are the section and plans of a reverber¬
atory furnace for experimental purposes. In this furnace, the
fuel is contained in an interior fire-place ; and the substance,
to be submitted to the action of heat, is placed on the floor of
another chamber, situated between the front one and the
chimney. The flame of the fuel passes into the second com¬
partment; by the form of which it is concentrated upon the
substance exposed to heat, which is not confined in a separate
vessel or crucible, but placed on the floor of the lurnace.
478
DESCRIPTION OF THE PLATES*
When reduced to a state of fusion, the melted mass is allowed
to flow out through a tap-hole at h. The dimensions of this
furnace it is scarcely possible to state, as they vary so consi¬
derably in different parts of it ; but they may be ascertained
by referring to the figures, and by the application of the scale.
In all three figures, a represents the ash pit ; b the grate com¬
posed of moveable bars ; c the door at which the fuel is intro¬
duced; d a door in the side of the chamber, for the purpose
of inspecting the process ; e the floor of the furnace which de¬
scends, and is gradually contracted towards the back part;
f another door for introducing and stirring the materials ; g
the back part of the furnace, immediately under the chimney;
h the tap-hole ; i the chimney.
Figs. 69 and 70, exhibit a cupelling or enamelling furnace .
The form of this should be an oblong square ; its dimensions
being regulated by that of the muffle, which should go home,
to the back, its front edge lodging on the mouth of the fur¬
nace. On each side of the muffle, two inches and a half must
be left, to let the fuel pass readily underneath, where there
should also be a similar space. A stoke hole must be left on
the other side, but the situation of the view will not admit its
being shown. Before the muffle, is a projecting ledge or shelf,
shown at <?, which is intended to support any thing that is to
be put into the muffle. Two twelve-inch tiles, worked in
along with the bricks, will answer this purpose. In both
figures, a shows the ash pit ; c the grate ; d the muffle ; e the
opening for introducing the muffle ; f the chimney, and g the
cover.
Fig. 71. Sand pots with rims of different sizes.
Figs. 72, 73. Dr. Black’s portable furnace, made of sheet
iron lined with fire clay. Its dimensions, as they vary in al¬
most every part, will best be learned from the scale ; a the fire
place ; b the chimney : c the ash pit ; d the door of the ash
pit ; e a register for regulating the quantity of air admitted to
pass through the fuel.
Fig. 74. Mr. Chenevix’s wind furnace. This is rudely
sketched in Nicholson’s Journal, from which the more accu¬
rate figure in plate viii. is taken. This furnace Mr. Chenevix
describes as follows : 66 I have constructed a wind furnace,
which, in some respects, is preferable to the usual form. The
DESCRIPTION OP THE PLATES.
479
sides, instead of being perpendicular, are inverted ; so that the
hollow space is pyramidal. At the bottom the space is twelve
inches square, and at the top only eight. The perpendicular
height is seventeen inches, from the top to the grate. This
form unites the following advantages. 1. A large surface is
exposed to the air, which, having an easy entrance, rushes
through the fuel with great rapidity. 2. The inclined sides
act as reverberators. 3. The fuel falls of itself, and is always
close to the grate.”
In the figure, a represents the grate ; c c are two bricks
which can be let in at pleasure, to diminish the capacity : l is
another grate which can be placed on the bricks c c, for occa¬
sional purposes : d d are bricks, which can be placed on the
grate b9 to diminish the capacity of this part of the furnace ;
e the cover. Both set of bricks should be ground to the slope
of the furnace.
In the construction of every furnace, which is intended to
produce a strong heat, lime or mortar should be avoided, and
the bricks should be set in loam, or Stourbridge clay, worked
up with water and sand, inserting occasionally pieces of sheet
iron, bent twice in opposite directions at right angles* The
furnace should be allowed to remain some weeks, after setting
up, before it is used ; and before raising a strong heat, a gen¬
tle fire should be sometimes kindled in it, the strength of which
may be gradually increased* When a strong blast is expected,
it is necessary to bind the brick-work together, externally, by
strong iron bars and plates, kept in their places by screws.
The chimney should be nine inches wide, and raised to as
great a height as circumstances will admit.
The coke of pit coal is the only fuel fitted for exciting an
intense heat, and should be used in all cases, except in the
reverberatory, and in distillations with the sand bath, when
pit coal may be employed. The charcoal of wood is adapted
principally to portable furnaces.
PLATE IX.
Fig. 75. The galvanic battery called couronne de tasses ,
described vol. i. p. 188.
Fig. 70. Apparatus for obtaining the elements of water in
separate tubes ; see vol. i. p. 195.
480
DESCRIPTION OF THE PLATES.
Fig. 77. The pile of Volta ; see vol. i. p. 187.
Fig. 78. Section of a galvanic trough, to explain the
theory of the excitation of galvanic electricity; see vol. i.
p. 207.
Fig. 79. Apparatus for obtaining oxygen and hydrogen
gases, from separate quantities of water not in contact with
each other; see vol. i. p. 196.
Fig. 80. Two agate cups connected by moistened amian-
thus ; see vol. i. p. 198.
Fig. 81. Two gold cones similarly connected, ibid.
Fig. 82. Agate cups similarly connected with an interme¬
diate vessel i ; see vol. i. p. 198, 199.
Fig. 83. Apparatus for procuring potassium from potash
and iron filings, described vol. i. p. 220.
Fig. Si. Apparatus for firing gases by electricity, or sub¬
mitting them to electrical discharges, vol. i. p. 123.
Fig. 85. Pepys’s improved gas-holder : a a small iron re¬
tort placed in the fire with a jointed conducting tube l , which
is admitted into the vessel at c. This is shown on a larger
scale in a different part of the plate. The letter d is placed on
the body of the reservoir, and near the central pipe, which
descends from the cistern e to nearly the bottom of the vessel.
At f a glass tube is fixed, which shows the height of the water
within the vessel. When a jar is intended to be filled with
gas from the reservoir, it is placed, filled with water and in¬
verted, in the cistern e. The cocks 1 and 2 being opened, the
water descends through the pipe attached to the latter, and
the gas rises through the cock 1. By raising the cistern e to
a greater elevation, any degree of pressure may be obtained;
and a blow-pipe may be screwed on the cock at the left side of
the vessel.
END OF THE FIRST VOLUME.
C. BalJwir, Printfr,
New Biidece Street, L ml an.
PI .1.
London. Published ty Baldwin. Oadack Sc Joy, tcR-Hunter.
FIJI.
London .FubUdhed ty Jiaietoin ■ (radodc Sc Jot/, k R.Bunter.
f.ondon FuvhsTud by JkUtbrut- Gu<fcc/c £■ Joy. Sc RJtunter
r/.jr.
lowry soulf
HoruloruPub fished by Baldwin.. Gudoclc k Joy. k Ji. Hunter.
7V V.
— I Inches
lowry sculp.
Zondon RiblishccL by Balckvuu OadockkJoy. kRJIunlci-
JP l VI.
£/>wiy sadfj.
£ondon. I'ublidud l>r Hii/tlwin . (judoc/c k -Toy <> /( .Hu/iUr .
ti . m
Xowry sculp.
ZtmdonJ^tMished l>y Baldwin. Cradock k Joy, k It. Hunter.
ti.thi.
londonMlished try JiaMwin Qndodk & Jov SoJLHunter.
I
-
Fl.JX.
lowry scu/p'
LffndtnvFUblzj/ud by JlalAvUi Oadock k Joy. k ILHimUr.
Live Music
Archive
Librivox
Free Audio
Metropolitan Museum
Cleveland
Museum of Art
Internet
Arcade
Console Living Room
Open Library
American
Libraries
TV News
Understanding
9/11